A mud and snow tread is a soft compound. Not going to wear long, or last long. Replace with a highway tread if you are going to trailer with the truck. And get an alignment. But suspect the problem is the M+S compound, it just does not last.
I bought a M+S tire for my 1987 Toyota Xtra Cab, once. I got 16,000 miles out of the set. Went back to Bf Goodrich A/T KO's and got 70,000 miles out of that set. That's how soft M+S tire rubber compound is, and how fast it wears. Even in a light Toyota pickup truck, with no trailering.