If you are talking about the RW382RL or RW3821RL the 17900 GVWR puts you over the SRW RAM rating. You will have to really watch your loading to stay under RGAWR with all three SRW. I am towing a BH3575el(39'4") 5th wheel with 16K GVWR and I am pushing the truck close to it's max ratings. Dually would be a better choice. If Ford can handle a lot more as Troy stated, I would like to know the RGAWR. I do not believe there are 18" or 20" tires that can handle more than 3500 pin weight. Tire ratings are the most important to make sure you are not exceeding. Chris