Transmission does not have first, reverse or overdrive

If it is a 4L60E it could be a few things, most common for loss of those gears only = sun shell failure. Lo-reverse clutch pack worn out or blocked apply circuit to the piston.
Best option is a rebuild with a beast sun shell and heavy duty clutches. Next would be to replace with a remanufactured or used transmission depending on what condition the truck is in.

If it is a 4L80E the low and reverse band anchor pin is a likely issue. They can break or the case fails.

For both the losses can also be electrical and should show up on a good scan tool. It could be failed solenoids or bad wiring if that is the case. A good visual of the wiring and transmission connector and scan should show if those are the problem.

Thank you. I had a buddy of mine who runs a local shop. The way he explained it was it was a common problem because we had snow and ice recently. He continues to tell me that water gets into the connectors for the transmission causing it to fail. I unplugged all connectors and cleaned them. Took the negative post off the battery for the night to reset codes. Did not work!

Water in them can cause problems. If he has a decent scan tool he can probably check to see if it is electrically related.