Hello , check wiring and voltage on solenoid forward/backward. If you see a the solenoid goes out of function you have a wiring issue. Check the little relays for shifting and the wiring. I have some trucks with a wring with corrosion in a connector behind the relay box and give same problem issue
It comes on momentarily but then goes out. Disconnecting the seat switch does not generate any fault codes.
You can check the shift lever contacts for dirt , dust or burn marks. Remove steer wheel and 2 screws on shift lever and harness plug. Also , outside temp Has caused some failures in the shift relays located in the box below left step. Front left corner. Use heated relays for repair. Use the orange handset to monitor seat, travel functions and seat in the I/O sections. Does the fork light come on in the dash upon no travel??