Ive got a reg cab 4x4 and am wanting to put a set of bfg's LT285/70R17D1 121Q W km2 mud tires on this truck. My question is, does the air pressure sensor adjust to different tire sizes or will it be jacked up???

 

If the air pressure is to high or to low it will set the tire pressure light. I think you have a 17% plus or minus threshold.
You can have the dealer reprogram the remote control door lock reciever (RCDR) with a tech 2 to your new tire pressure settings.