hi all.
the body of the car is in the way. however, there is a way. i saw a guy on youtube do it. he had to jack the car up pretty high, disconnect the steering column shaft, remove wheel, strut, half shaft, then loosen some of the engine/tranny bolts on the engine support frame that holds them up, this allows you to lower the engine and trans for more room. then loosen or take off the trans mount on that side. and then he could unbolt the trans side cover and barely slide it out and up. very tight space. don't go by what I say here, watch the video. there might be a couple of them. then you can access the side of the trans from the wheel well.
there'* more than I have mentioned here, just giving you an idea of what'* involved, it'* a very big job.
here'* a link
his channel is "m ph"
hope this helps!

I drove the car again Sunday. I backed up the driveway and turned around. I decided for good measure to stop and turn the engine off. Then I started, backed up a short distance, then put it in drive (O), and proceeded to the end of the driveway; about 25 feet. I stopped, check for traffic, then turned right out of the drive up the slight incline. As soon as the trans went from L to 2nd I felt the stumble and knew the torque was locked up. I drove it about a mile to a place I could pull over. I shut off the engine, waited, started the engine, put it in reverse, backed up, forward out of the lot and everything was fine. I drove it about 12 miles, no problem. Stopped at a shop to do a bit of shopping, came out, started, no problem. I drove it about 15 miles to another shop, shut off, did shopping, finished, drove the car, no problem. Drove to another location about 10 miles away. Stopped and did some errands. Started the car again, drove about five miles, did some shopping, no problems. Went to my sister'* house and spent the evening with her; about four/five hours sitting. Left my sister'* house and drove the car home about 18 miles no problem. This involves lots of stopping at signs and lights during the trips.

Now I have been looking at this as if the torque converter locked up under normal circumstances and then failed to release when I had to come to a stop or slowed down. However, I am now thinking for some reason the computer is commanding the torque converter to lockup when it shouldn't. I think when I left my driveway, the computer commanded the lockup for some strange reason. What are the normal conditions for the computer to command the torque converter to lock up? I think this is the approach to solving the problem.

I have the ScanXL; not sure which version, on my laptop with an adaptor to connect to the data port. Is there a way I can set it up to do data recording of what is happening with the computer and trans?

I replaced the tranny by myself and installed the replacement by myself. It is a job. I decided to drop the tranny leaving the engine in place by splitting the cradle. On this model the cradle can be split. There was enough room to slide the trans over and then come out down below. I used an engine support that I fabricated to support the engine from above; the engine has to be supported by some means to drop the tranny. There is a "reverse" bolt in the torque converter housing that can only be reached by long extension bars inserted across the car from the passenger side wheel well. Yes, I did reinstall that bolt; I don't believe in cutting corners. If that bolt didn't need to be there, GM wouldn't have spent the money putting it there. I spent a long time working on the car and had to beg rides during the time. When I got in, I found other things as well, replacing ball joints, inner and outer tie rods etc. All the mounts; engine and trans, were worn out and had to be replaced. New struts on the front. I basically repair the whole front end of the car at the same time since I had to remove so many things to drop the trans.

Update: Today I drove the car without any issues. I drove 18 miles to my sister'* house, spent the day there, returned home. No problems on the way there or the way back. Today was a nice warm day. I am wondering if it has anything to do with cold? I still think the issue is the computer is commanding the torque converter lockup on when it shouldn't.

None of them will command lock below a certain speed, usually 35-40MPH, unless someone has botched the programming or something. Often, they also won't command torque converter lockup until they have engaged their top gear (4th in your case) or the top gear available (like on some cars if you limit the transmission to 3rd in a 4-speed, they'll engage the TCC in 3rd after a few seconds of engagement if conditions allow). I don't know of any mainstream cars that will allow, let alone command, torque converter lockup in 1st. You haven't mentioned an erratic speedometer so I infer that the VSS (that is used as part of the PCM'* decisions) is fine.

Since the same computer worked properly with the previous transmission, I am removing this possibility from my troubleshooting tree.

It still sounds like an internal hydraulic leak to me.

Cold day things contract, leaks happen. Warm day things seal up, less/no leak(*). This seems to go along with your observation that you have the problem early in a day'* cycle, then after a reset it does fairly well for the rest of the day. Keep in mind, the leaks I'm talking about are very small, and are all that are needed for transmission issues. If a tiny bit of pressurized fluid leaks from one hydraulic circuit to another in the valve body (or other places), all kinds of interesting stuff can happen.

I wasn't gonna post this cause y'all will think I'm crazy.
I swear this happened!
91 Toronado. I had a similar issue over the past year. The car would jerk and buck like the torque converter was locked up and it was dragging the engine down. At first it was intermittent, but it gradually got worse, until it was doing it all the time. So about 3 weeks ago I got mad and was getting on the highway, so I floored it. Got on the highway, made sure it was clear and kept going until I hit 80mph.
It has not done it since! Now, this car sat for about 2 years, except I would drive it around the block every month or so. didn't even get up to temp. but I drive it all the time now. No more problems.
It has the 4t60e in it.
I'll let you know if the problem comes back, but so far so good!
Kimberly, you might want to try something like this. Though I take no responsibility. Be careful! I was on a deserted stretch of highway late at night.

I don't think you're crazy. I can totally see this happening in some cases. I wouldn't put a guarantee on it, but it'* worth a try. In safe conditions of course. With a professional driver on a closed course. Results may vary. Past performance is not a guarantee of future outcomes. Use as directed. Yada yada.

That having been said, this one tastes like valve-body hydraulic circuit cross-leak to me, whereas the Toronado tastes like sitting forever allowed a piece of crud to build up and a good flogging pushed it through like a kidney stone.

I find it strange that the cross leak happens on the way out my drive but disappears after only driving it a mile and doing the engine off routine; that is not time for parts to heat up and expand; and expansion of metal increases clearances, not decrease; metal expands on heat; this is happening when the trans is cool. I also find it strange it happens when I turn right up the incline but not left down the incline. The other area is also a right up an incline. I might see if I can get the wiring harness out of the loom and give it an inspection when the weather clears up. At the moment the tractor is in the shed incapacitated and can't be moved. It sounds to me to be something commanding the torque converter to lockup. Pulling out of my driveway is low speed. That is why I asked about the ScanXL software if anyone has it; can I see such things as if the torque converter is locked up etc from the scan tool?

First I feel it important to remind:

I suspect this based on the symptoms and circumstances described. This is still Internet troubleshooting so nobody here comes with any kind of guarantee, not even me.

Yes it is. The torque converter warms transmission fluid, as does general operation and thermal transfer from the engine block. I'm not talking about a gaping hole here. I'm talking about the potential for an extremely-tiny bit of extra clearance between a hydraulic circuit running at a hundred or two PSI and another that is unpressurized or at a lower pressure. This could cause a check ball to move the wrong way or backpressure in a circuit where it isn't expected or who knows what else. These circuits are all side by side in the valve body and are also going through shafts and constrained by spinning seals that are also separated by tiny bits of clearance. Or maybe the fluid can't quite get somewhere it is needed when cold, and slightly warmer it can as the viscosity goes down.

Metal expands with heat. I agree. Metal that is held against other metal (by fasteners that constrain outward expansion) is pressed inwards by the same heat expansion. When we're talking thousandths of an inch of clearance being too much in between valve body halves and plates, a little heat expansion might just be enough to seal something up. Works out perfectly as an explanation of why the issue doesn't happen when warmed up. The same thing happens with a leaky exhaust manifold gasket (for example). They will often be louder when cold and quiet down a bit (or all the way) as they warm up. Metal and gasket material constrained between bolt heads and engine heads.

The transmission doesn't know the difference between left and right, except possibly if fluid is low and/or g-forces are high.

The transmission does know the difference between up and down. Sort of. It knows when going up that there is increased torque from the engine, therefore increased hydraulic pressure, when going uphill.

Worth a shot.

The only thing doing any commanding is the PCM that was commanding the previous transmission that was not doing this. Also the same PCM wouldn't command differently one mile later. Often, PCMs (and/or TCMs on models that have them) leave the torque converter unlocked until a certain temperature is reached as a method to warm up the engine as well as the transmission fluid more quickly.

I've got an idea: Before the next time you'll be facing the conditions known to cause this issue, start the car and let it idle for an hour (with the heater off) before departing. This will get everything mostly warmed up before it even moves. By doing this we can discover if it is a first-start-of-the-circadian-day thing, possible a temperature-related issue, or some other issue.

I can't speak specifically for the ScanXL product, but with a correct tool you would be able to see whether lockup is commanded or not and how much slip there is across the torque converter. Zero slip, or equivalent in and out RPM measurements, would tell you that the converter is locked.

The issue has gone away now that warm weather is here. I may get it to happen at times but overall it does appear to be an issue related to cold weather.