Buy a diesel for sheer grunt & pull. But as others have said, both modern gassers and modern diesels, the engine will easily outlast the rest of the truck.
In any case, gassers have been getting longer-lasting and diesels of been getting less so; they have been converging, as it were. Back in the 60s and 70s, gas engines were good for 100K miles, and would need a rebuild, rings, valves, seals, the works if they managed 150K. Diesels of the day were expected to go 400K-500K before needing a rebuild.
Today, both will easily do 200K, and very, very few truck bodies, electronic accouterments, seats, etc. will last much longer than that.