Other than dry, summer, street only applications, I've found OEM truck rubber to be crap.
BFG All-Terrain T/A KOs aren't great in mud (known fact), but are still better than factory rubber (Goodyear Wrangler RSAs for example). I've personally had about 6 sets of them with nothing but excellent results, especially in snow and wet conditions. I typically went up a size (about 1" in diameter) and would routinely lose about 1-1.5 mpg (acceptable to me given their performance improvement). This was on everything from Ranger Extended cabs to Dakota Quad Cabs, to Ram 1500s to F-150s. Longevity-wise, the least amount of mileage I've ever gotten out of a set was 72,000 miles and they still had tread just barely above the wear bars. The most I got out a set was 87,000+ on my Ranger. I always run staggered pressures and rotate them every other oil change (this is key in my experience). My dad has been running them for decades on all of his work trucks (F-250s and F-350s) with similar results. He typically gets about 55,000-60,000 miles from a set. However, he was always hauling loads and/or pulling trailers.
And if BFGs suck so bad, why do OEMs use them on some of the most expensive trucks they produce?
I understand there is always a trade-off with everything. My opinion is that OEM truck tires generally suck.
Sorry for the side track...back to Raj's car not fitting 315s.