[4uweque]

Just upgrading to a 2500 will get a much safer towing situation but won't get any better mileage unless you get the diesel. The diesel is the ultimate because it will last longer, use less fuel and have plenty of power as well. The one problem is diesel itself is normally 30 to 50 cents per gallon more and the initial cost of the truck will be a lot more than a similar truck with a gas engine, but will have better resale value. Only you can weigh the pluses and minuses and decide if you'll tow enough to justify the costs.