Re: Towing with 3.7L
It's not really just about the horsepower. Engine and transmission cooling, axles, hitch, etc., are all matched to the power of the engine - if you just boost horsepower there is no guarantee the rest of the vehicle can take towing the increased weight.
In particular, I believe the 3.7 uses a different axle (3.07 vs. 3.73 axle ratio) than both the 4.7 and 5.7...that could be a limiting factor in what you can tow.
An extra 1,500 pounds is asking a lot out of a vehicle that is only rated to pull 3,500...