Backspacing is different between 99-04 and 05 and up. You can get wheel spacers to run the newer wheels on an older truck. Lots of opinions about wheel spacers though. I'm sure someone will chime in with an opinion regarding those.
I had good luck with the bolt-on spacers I used on my 2002. I took my chances and bought them off ebay. I got lucky I guess. I ran them on a lifted truck with 38x15.5R20 Mickey MTZ's without any problems at all. Just my 2c