Gross COMBINED Weight Rating (GCWR) is 20,000 if this V10 is in an E450 (wuth a Four) chassis. Ours is and we tow a Nissan Frontier that's a little heavier than a Ranger. The Frontier weighs about 1000 more than the Mitsu Mighty Max (like a Dodge D50) that it replaced and we can feel the difference. But that weight in no way incapacitates that V10.
Toad is an "odd" weight, because there's no tongue load but it can still try to "wag" the back of the RV. It's carrying all its own weight, but should have a braking system. To use our coach (signature) as an example, its brakes are rated at its Gross Vehicle Weight (GVWR) which is 14500, NOT the CCWR of 20000.
If your chassis is E350, the gearing's a little taller. Since tires are same as E450, the E350 will labor more and bog a little sooner (wanting to downshift) on a grade/with more load.
Also, if you don't have TorqShift (the 5-speed with Tow/Haul not simply OD Off), it'll probably want to downshift more often than the 5-speed (known as TorqShift).