I put 285/70/17 Goodyear Silent Armors on my truck this spring. I have noticed no difference in mileage or performance in either DD or towing. What I have noticed is a better ride. Now, I went with (after Careful consideration) D rated tires, for more sidewall flex. My travel trailer is a pull type weighing 8,000 loaded putting about 600 on the hitch and we carry about 1,000 lbs in the box as well. I like the stance and the ride, we'll see how they wear.
Pulling a 5ver, I think that you'd want to stay with the E rated tires. You are putting far more weight on the truck than I am. The taller sidewalls on the 285s will give you more flex and soften the ride some.

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2007 Ram 2500 QC 4x4 SLT TRX4-Offroad 6.7L Automatic. '08 Jeep WK 3.0L diesel-wife's DD.
1998 Jeep ZJ 4.0L Automatic Selectrac-project for our son. '98 Jeep XJ-my wife's former DD.
1965 Dodge Polara 880 Convertible 383 Automatic.