Our 2012 HT 26.5 RLS came with D rated Goodyear Marathons and, so far, we haven't had a problem. Took a 3,500 mile trip with them last spring through Idaho, Nevada, California and Utah and they performed fine. Kept them aired up to 65 pounds and didn't exceed 65 mph at any time. In California, a good deal of the trip there the temps were in excess of 100 and I was very anxious, but they worked good. As long as they perform, I'll keep them on, but will probably switch to something else when the time comes.
2012 GMC 2500HD D/A Crewcab
2012 Jayco Eagle SuperLite HT 26.5 RLS
2009 Crestliner Superhawk 1900
2013 Polaris Sportsman 550 EXP
2008 Polaris Sportsman 700 X2