I have an 03 2500HD that i'm putting a fabtech 6" lift. will 315-75/16 on 10" wheels fit without rubbing? or do I need to run 305's. I don't like the sucked in look of the 8" wheels that well. I'd consider minor fender mod. any info would be apprecciated.

Most guys with a 6 inch run 35s. You should be fine. Look around a bit and you'll find a lot of pictures of trucks set up the way you plan to.