Gas is not good for towing anything more than 3,500lbs - just not going to get any gas mileage.
Diesel is the way to go. A diesel engine is 30% more efficient then the gas one of the same displacement due to the high compression ratio. I purchased an 05 crew cab silverado 2500HD 4x4 6.6 work truck... It has NO options except AC. The sticker was amazing cheap. It turned out that this work truck new was cheaper than most used trucks. Look at the chevy work truck.. they are hard to find but you can find them. (rubber floor etc.)
It tows awesome and I get great gas mileage. Without towing I can get over 19MPG. I have owned 7+ chevy trucks over the years and this motor and tranny combination is amazing. The alison has a "tow" setting and it down shifts to slow you down etc. Best tranny I have ever had.
It is a full size truck so it's bigger then the 1500 but when it comes to towing the full size pays off. Round town its probably bigger then you want. Gas mileage is going to always be 30% better with the diesel.
just my .02
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at least in my case, my truck does daily duty as well as towing. getting something as bare bones is that isn't too liveable on a daily basis. not to mention many of us can't plop down 20k for something we'll use about 8x/year.