Even my father's 98 1500 likes E rated tires better. The two extra plys really do make a difference in ride, wear, and load. If you ever notice, when a D rated tire starts to get worn, with 20 or 30 k on it, the sidewalls will start bulging. E rated tires dont do that.

 

Having run both on various full-size trucks, I greatly prefer the load capacity, handling, and tread life of an E-rated tire. Especially on a 3/4 ton truck or larger, I'd always go with at least an E.

I'm surprised they're telling you the D and E have the same load capacity; sometimes they're close, but it all depends on the exact size, etc.