I know for a fact that the 2003-2006 seats will physically fit and bolt into the 2001. I have a client with a 2001 Silverado 2500 HD and she has 2003 seats in it that I detail for all the time. Not sure how she got the wiring bits to work, but they do work. I can move the seats back and forth while I’m vacuuming. So I’m not sure if you’d have to make a harness and splice together to make work or if they’re plug and play. I also suppose it depends on which power options the seats have and which power options the seats in your truck have. Different seat options might affect what the harness looks like. Your best bet is to look in a junkyard and see what the harness looks like in a 2003 truck versus what your 2001 harness looks like.