I have a 2000 Silverado 1500 5.3 automatic 4x4. I recently replaced the transmission with a known good used transmission. I watched it drive into the shop. I installed a new torque converter and filter before installing the transmission. I pre filled the torque converter and filled the trans prior to starting the truck. I refilled to proper level after the fluid level dropped.
I went to run it through the gears to purge any air and it will pull down the engine RPMs but won’t move the wheels. I put the trans in neutral and the truck will free roll.
I checked for flow at the trans cooler lines and have good flow. I checked the transfer case to make sure it wasn’t in neutral, the truck won’t move in park so transfer case is in gear.
I can’t figure out what I’m missing.
Do I need to change out the solenoids in the valve body or have the transmission control module flashed?