Where is the TCM located?

The TCM is a part of the powertrain control module aka engine computer located in the front of the truck under the left battery box. All of the shift control solenoids are inside the transmission, you need to drain the fluid, remove the pan, then the transmission valve body and then you have access to them all. What is the issue you are having; it may be possible to give a better answer if we know the problem.

That sounds like a bad remanufactured transmission then. If you put it in park with the wheels on the ground can you push it around? That would tell you if it's the trans or another item. If the park pawl holds it then your differential and T-case are OK and connected but there is an internal fault with the transmission, likely pump or pressure regulator not the TCM or solenoids.