Hello! First time posting and it appears I am having a very common problem with the transmission in my 1999 Pontiac Bonnevile SLE, I will try and post all the information that I can. The transmission is a 4T65-E with the 2.92:1 M15 gears. The transmission has began to shift really rough to the point where it feels like its slamming in and out of every gear (I have tried both manually shifting the trans and also letting it shift on it'* own with no difference). When the problem occurs I can hear the transmission pump whining which is telling me that the computer may be commanding max line pressure in the transmission. When this happens I can shut the car off for a miniute or two, and fire it back up and run down the road a few more miles before it starts it again. When it'* not shifting hard it seems to shift perfect so I am not seeing whats causing the problem. This started out of no where with no other problems present. So far to try and remedy the problem I have drained the transmission and changed the filter and filled transmission with new clean Dexron III fluid (there was no particles or metal in the bottom of the transmission pan although the fluid was brown and smelled burnt), I have changed the EPC and the TCC PWM solenoids, and have added an external transmission cooler. The shop that did all the work installed the external cooler inline infront of the original cooler (I don't know if that would cause a problem or not?). After all this work was done the problem still persists, I have yet to try the shift improvement kit from ZZPerformance as I do not know if that will fix it or not because I have been told that it could be caused by a stuck or sticking valve in the valve body. I would to like to hear any and all information that anyone has that would be helpfull in fixing this problem because I am out of ideas as to where to look or what to try next. Help me keep another piece of the Pontiac legacy on the road, any help is greatly appreciated.

That sounds a lot like my transmission, but more severe... I still have no answer as to what is going on

You need to attatch a scan tool and a pressure gauge (to the line pressure port) to see what is actually happening. It sounds like an EPC problem, but since you already changed it, it doubt it. You may wanyt to check your mass air flow sensor as that will effect main line pressure.

Ok, I have an update on the problem, I hooked a scantool to the Bonneville and recovered 2 codes from the transmission computer. First code is DTC P1811 Maximum Adapt and Long Shift and the second is P0719 Brake Switch Circuit Low Input. I did a little bit of research on the codes but correct me if I am wrong, the P1811 is normally for the EPC solenoid, the P079 has something to do with the TCC circuit. The shop I took the car to said they changes both the EPC and TCC solenoids, and I was told they are both in the same area in the transmission, behind the side cover. Now If they are both in the same location, are the connectors for the solenoids both in the same wiring harness? if this is true is it possible the wiring harness to these solenoids could be bad? The problem started all of a sudden out of no where with no other problems occuring. The service tech that looked at the car also drove the car with the computer hooked to it and said the long shift was occuring between gears 2 and 3. Could it be a broken accumulator spring, or possibly the clutches in the 3rd clutch pack? The car is going in the shop Tuesday to be looked at further, their going to remove the transmission filter and break it open to look for clutch material inside the filter to try and rule out the clutches being the problem. Any input on the problems would be greatly appreciated!

The long shift is something that pops up now and then on these transmissions. It can come from worn clutch plates. Installing a shift kit will shorten the shift time and clear that code. That wont address the fact that the clutches are a bit worn out.

Even a correctly assembled transmission using factory specs MAY set a P1811 as GM leaves the 2nd and 3rd clutch packs loose. GM does not even give a spec for clutch clearance for these 2 packs.

We use 1 or 2 oversized steels for the 2nd clutch and use early (thicker) 440-T4 plates for the 3rd clutch with excellant results.

Ok, its been a while since I posted but I got a verdect to the problem with the transmission. I had the fluid changed in it again thinking that maybe there was debris in the transmission. The shop I took it to recommended breaking the old filter open to look at the filter element. Well when they broke it open in front of me the filter was full of large particles and the tech said it was material from the clutches. So at 150 thousand miles it looks like I am in line for a rebuild. My next question, where is a good place to have the transmission rebuilt. I don't know anyone that rebuilds them so I know I'm not getting out of this cheap but I am hopeing to get it rebuilt for arround $1000 dollars. Is that price even realistic? I just bought the car in February for $2200 dollars and I'm hopeing I don't have to sink the cost of what I paid for the car into a trans job. Any advice and information would be greatly appreciated.

Would you be doing the removal and install yourself? If not, $1,000 isn't overly realistic based on the amount of work to remove and install a trans. A trans shop will take a couple hours for removal and a couple for install.

Factory labor time to remove, rebuild and install is about 17 hours, plus parts, fluid and incidentals.

If you can do the work yourself you can get in that area. I did a trans swap here a few months ago. He found a low mileage trans at a salvage yard for $500. 13 hours of work later it was driving away. Could have done it in about 9 or 10 without his help.