I have an 05' F250 Crew Cab 4wd w/ the FX4 package (has V10 motor) with about 53k miles on it. The prior (and original) owner replaced the OEM BF Goodrich tires on it for Firestones! The Firestones are about shot and must go. Current tire size on it is 285/75 R 17 (stock wheels) and I just kind of assumed he replaced the tires with stock size. Well the door panel says 265/75 R 17 is standard. Which is right??

If 265's are the standard size, will I see any noticeable improvements in power/accelaration going back to a smaller diameter tire? My truck is an Auto w/ the 4.10 gears.

BTW, I'm pretty dead set on Michelin LTX tires as I've had great luck with them in the past. However, I'll listen to suggestions! Truck sees little off road use, but Colorado winter roads often. About 85% on pavement highway or town driving.