P0894 Transmission Code 05 Tahoe Z71

[Huckster]

I have an 05' Z71 4x4 Tahoe with 134K and since I have bought it if I drive it over 90 minutes it the transmission will go into limp mode and shift firm and it will show a P0894 code(transmission components slipping). Now it will do it after about 20-30 minutes of driving. I feel no slipping and it shifts normal until it spits the code and goes into limp mode. If I cut the car off and restart it resets and goes another 20-30 minutes. I have done some research and have found it could be electrical, torque convertor, PCM, etc. Fluid looks good and smells good. Don't know how long since last service. Anybody with similar symptoms and ideas. Also what year 4L60e's will interchange into the 05' Tahoe. I have an 04' I put a 6.0L in and may just swap that trans into this one to sell and put a 4L80e in the 6.0 Tahoe.