Sounds like possibly a ground issue somewhere maybe. I just recently had a ground go bad on my 03 and all of the sudden lost ALL power to inside the cab of the truck, it sucked! Obviously a little different situation with mine but I know these trucks with some years and miles on them can have some ground issues in general.

 

Pretty much every single wire on this truck has been modified, completely "custome" harness with multiple grounds. EVERYTHING is grounded to EVERYTHING else, so I highly doubt that's it

 

Well that's good, sounds like you have that part covered! Narrows it down a little for you then I guess.