How much weight do you tow? and with how much motor?

We have a 36' 1998 Monaco Windsor with a 300 hp Cummins. We tow a 2500 lb Honda Fit, 13 feet long, which serves all the purposes we need in a toad, including a great more cargo space than it looks like it would have. We barely know it's back there, on the flat or on hills. The toad costs us about 1 mpg - about 10 without it, 9 with it. Part of the reason we went for a DP was to have plenty of pep on hills, and this rig has it.