1997 Ford F-150 1997 F-150

Okay, so my truck has a few problems, the truck runs and fine and has tons of power but my check engine light is on, it reads throttle position sensor low input, so I replaced it and its no different whenever the code is reset the light comes back on after I start the truck again, also my 4wd wont work, and it will not down shift at all unless I do it manually, there are no tranny codes and I replaced the GEM and the PCM but nothing has changed, all my fuses are good and I was told that the speed sensor drive gear wears on them, has anyone ever heard of that? Any help would be greatly appreciated, thanks