Lost of good responses, and I agree with most of them. A few points in agreement with the above:
Everything in the suspension system affects ride, Tires and Springs together for sure. Firmer springs with high tire PSI makes for a stiff ride, and sometimes poor traction. I prefer to have softer springs and tires if they will work for the application. Adjust both for ride quality as needed. Lowering tire pressure to a reasonable PSI for the load is the easiest, least expensive, and fastest option.
The LT265/75R16 size is designed to carry 1,910-pounds per tire at 35-psi cold per the load inflation charts. That is a sizable load, even for what most consider 'heavy' rigs. (Weigh your vehicle to know the 'facts', there is another active thread on weighing your rig.) I have a very heavy outfit but rarely pump 265/75s above 35-psi (when pulling heavy trailers/lots of tongue weight), and often run them at 30-32-psi, just enough to keep the TPMS light from coming on.
Personally I do prefer the ride & flex of a load range D tire over most "E"s, but many tires are only available as a LR E, and I believe this is the future, more "E"s and less "D"s. As someone noted, a LR E is better for most of the heavy-duty pickup users who buy more off-highway/truck tires than the SUV crowd (my guess). As LR D tires get updated into LR E designs we will likely have mostly LR E and some LR C tires to choose from in the most popular sizes.
My preference for load-range D tires aside, I'm currently running a 265/75R16 LR E tire because that is what's offered in the tread I wanted. I wouldn't sell your tires unless you really hate them. I would weigh your rig to insure you can safely run the lower PSI some are suggesting, then experiment with 30-35 PSI. If that doesn't do the trick, then play with springs.
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