I have a one-block hill near home that is probably 25%, maybe a little more. I tried it once towing my fifth wheel, and I had a traction problem with rear wheels slipping. My total weight is 20,000 lbs., with (a guess) 5,000 lbs. on the rear wheels, which would make 25% on rear wheels. To have enough traction for that grade I think that I need to add 500 or 1,000 lbs. to the bed. (That would be no problem for a F350.) Anyway, to avoid slippage going uphill on a 25% grade, I think it would be a good idea to have the rear wheels carry 30% or more of the combined weight.