I'll make a long story short. Remember the '97 Eighty-Eight i did the intake on? You guys were great on that. New problem (again, possibly major). I took the owner out to Soiux Falls SD tuesday night and drove back right away. 560 miles round trip non-stop. On the way back i wanted to make good time and i had a full tank so i pushed 'er to 100 and hit the cruise. Well that went fine for about 50 miles until the tranny popped out of lock-up and OD and sat in third. I couldn't get OD back. Slowed down to 70, set the cruise. It went back into OD but the RPM'* would just climb and climb and climb. So i drove it in 3rd at 70 for about 20 miles and decided to try OD again. Shifted up, went into OD and lockup fine. "Guess it was a fluke!" and i continue on my way. Noooo such luck. Falls back out of lockup, OD slips. I stopped at the next gas station, checked the fluid (full and not burnt), and continued my way. I deal with this the rest of the way home until about 100 miles away and it acts completely fine after that. My shifts themselves never slipped on accelleration, only when at speed. I didn't get a code until that last leg, and it was a code p1870. Any ideas pals?

Oh and details: it'* an early year, 4T60-e, with 61k miles on it.

Ok..here'* the code name
DTC P1870 Transmission Component Slipping

Most likely you were overheating the transmission. Our transmissions (I have heard, never read) have built in programming. So if the trans gets hotter than it'* programmed to do, it pulls 4th away from you. Typically this type of thing would be found on a long trip, and the er speeds could justify it.

So, this sounds like an opportunity for you to install an auxiliary trans cooler if you, or your friend, plan on driving at these speeds more often.

I understand the TCC slipping, but that doesn't explain why i was slipping in 4th gear also. Or is that related? I suppose that it would be a good time to install an auxiliary cooler. I'm going to go check out the car later today and see what i can find. The owner isn't here right now so i can't do much with it until she get'* back.

Well it must be a bad problem. I made the drive again today, and once again on the way back it lost 4th gear AND 3rd gear. 70 MPH yieled around 4000 RPM'*. I stopped to let it cool down and it seemed to be OK after that. I think she'* got big big problems ahead.

For about $60 you can get a trans cooler and drop your pan and replace about 1/3 of your fluid. It could buy you some much-needed time.

Could be a fluid pressure issue due to a clogged filter. You should drop the pan and change the fluid, install a cooler, might save it.
How many miles on the current filter?