Until recently I towed our 2008 Avalanche behind our American Tradition with the ISL Cummins rated at 400 HP. No problem. I did not notice any big change in fuel mileage either. Now towing a 2008 Hummer H3, but that decision was NOT based on curb weight. If I owned an Avalanche and wanted to tow it I would do it again.
I assume you have the C7 Cat engine rated at 330 HP, which I have previously owned in a 39 foot motorhome (Discovery). I do not think you would notice much, if any difference between the two vehicle weights that you mentioned. It's only 1700 pounds. I would definitely not let this difference force me to make an otherwise unwanted change in dinghy. Additionally and perhaps more importantly, my C7 powered coach had a better horsepower to weight ratio than my current coach with its larger engine, because as the engines get bigger they are mated with heavier coaches, until you get, perhaps, to the top end of the engine/motorhome combinations (500 to 600 HP) which neither one of us have.