Transmission

Unless something was missed when replacing the transmission, I would say that maybe the used transmission is as bad as the one taken off the truck. It happens, one never knows the condition of used parts until they are installed.

Have you checked the linkeage bushing? These little plastic bushing break easily. Dorman makes a replacement bushing.

Could be, but if the shift lever moves the bushing must be fine. But check them, one can never rule anything.