E LOAD OR D LOAD TIRES?

Go with what the tire guys are recommending.

The tire guy is trying to make a good sale! E load is a heavier load rating, if you dont tow you will be fine with a D load rating tire.

If you tow at all, you want E load. And just a suggestion, I have Firestone transforce A/T's on my ex. I keep them properly inflated, and I always rotate them every other oil change (so 6k miles) and I currently have 60k miles on them. I expect another 15k-20k out of them with the tread thats left.

Your tire guy is right. D load tires have too soft of a sidewall for you big X. The truck alone pushes the limits of D rating tires. The truck will handle better with E rated also, due to the stiffer side walls.

Get the E's but not the Firestone TransForce. Mine are tearing at the lugs and they want me to pay for a new tires after 5,000 miles. Other brands never gave me that trouble.