I am running 295/75 16 BFG ATko and they are great. I would not go to the 315 without a lift, nor would I go larger even with my 4. 10 gearing. I think they would be make the gearing to low and you would loose more performance than I am willing to give up. My next questin would be why do you want to go that big? What do you use your truck for? These are just the kind of questions I ask myself before a mod to see if I am being realistic.
Ted