what else could be wrong if stop lights stay on and stop light switch has been replaced

Well unless something in the tail light (like a circuit board) is bad then I would say warranty the stop light switch first as that is all that turns on and off the stop lights acording to the wiring diagram for your truck. I also need to ask if you have the tow package with taillight converter?

Improper adjustment of the brake switch can cause the problem as well. Check the pedal for a missing stopper for closing the switch.