Did you read the manual? Is the truck an automatic? If so is it in neutral when you are trying to shift? Are you stopped when you try to shift?
If you are doing all of that properly, you could have a bad switch, bad wiring or still a bad transfer case shift motor.
I don't remember where the info is, but I would start by checking voltage on all of the wiring and making sure the signal is getting where it needs to go. It could just be some corroded connectors from salt working it's way into them.
2006 F150 FX4 Super Crew - Bilstien 5100s leveled 2", 35" KM2s, 4.56 gears, Detroit locker, Eaton E-Locker, Traction Bars, AEM intake, Xcal 2
2010 VW Golf TDI 6MT