My 2003 2500 GMC 4x4 came stock with 265's 16's ... and I eventually went to 265 BFG, as I always do with tires - change out to BFG. When we bought the 2015 2500HD 4x4, it also came stock with 265, but 17's. The stock ride was horrendous, so bad that I almost sold the truck after a few months, thinking it was the truck and not the tires.
(After a long story I'll skip her) Eventually, GM dealer agreed the tires were bad and causing the instability, rough ride, and slipping/sliding in any kind of road moisture.
GM gave a credit, and we went to BFG AT KO 285 17's on stock rims which the dealer ordered and installed. The ride improved enormously on highway or off-road camping. Very smooth ride - and no thoughts now about selling it.