Hey guys, Have this Workhorse UPS truck with a strange transmission problem. This has the GM 4.8L and I believe the transmission is a 6L90, but not positive. Truck has been to 2 other shops and had 5 new transmissions in the last month. The problem is, the trans is shifting into neutral when in gear. This happens most consistently in reverse. After a cold start it will hardly engage reverse at all, but after warming up it usually stays in gear at idle but shifts back out if we accelerate. Occasionally this also happens in drive, so far has only happened for us when the truck was fully warmed up. Also, sometimes when we shift into gear, the engine will bog down or stall, like the torque converter is partially locked up. These problems seem to be electronic, as the solenoids are being commanded to shift to neutral. When it is operating normally the transmission shifts well with no signs of slippage and the fluid is brand new and full. The shop that installed the last transmission says they sent the vehicle info to be programmed into the TCM when they ordered the reman trans. Hoping someone familiar with these drivetrains can point us in the right direction. Thanks in advance.

James Kuhns
Owner/Technician
Auto Tech Solutions
Chatham, New York, USA