We use our F350 dually to pull a sailboat on a triple axle trailer between Wisconsin and Florida twice a year -- the trailer with boat weighs about 12,000 pounds. TireRack.com reviews are good for the Firestone Transforce HT but a couple local outfits recommend the BF Goodrich Commercial T/A as giving a better ride (plus they hate Firestone on general principle). Tread wear is less important to us than handling because we don't put on that much total mileage each year. Any opinions? Also, if we only buy 4 new tires, would you put the older ones on the front or on one side of the rear? Or would you just bite the bullet and buy 6 new tires? Thanks a bunch!