MH with highest tow capacity other than diesel pusher?

Any newer Forest River Class C motorhome will retain the full Ford 22,000 GVWR which minus the 14,500 GVWR leaves 7500 pounds for towing. You will have to upgrade the receiver though, and you really have to watch rear axle weights on a class C. That means go with a lighter weight flooplan (i.e. no rear slide) and get a long wheelbase. You can find 31' Cs with either 208" or 223" wheelbases, so it pays to watch the details.