I have a 05 Dakota with the 4.7 and a tow package. It tows my S&S fine, while getting 16 to 18 (high side) miles to the gallon. But on the other hand who really is thinking about gas mileage when we are driving a V-8 boat and towing them everywhere. If we were thinking about gas mileage would we even have a boat or would we be driving little Honda's and smart cars everywhere
Basically............If you don't want to get a new truck every 2 years, get what you want with the biggest engine you can now, something that you will be happy with and be done with it and keep it until it has 200,000+ on it.
Its always nice to have extra power that you don't use but it sucks when you don't have enough and need it.