No aftermarket gas fuel tanks to replace the factory installed tanks, only diesel fuel tanks. Reason I bought a 3/4 ton with the diesel engine was that with the factory 36 gallon fuel tank I knew I would get at least 30% more miles per tank of fuel when towing, as in 11-13 mpg versus 6-8 mpg with a comparable gas engine in the same truck.
Larger factory gas tanks are available with the Ford and Ram 1500 class pickups along with V-6 engines. Toyota only provides a gas guzzling V-8 at this time although a very large fuel tank is standard. With Chevy you have no option for getting a larger gas tank and so I would not advise buying on of their trucks for towing unless you go for the diesel engine.
Diesel provides greater fuel economy but the total cost of ownership is double that of a gas powered vehicle. You have to decide if it is worth the expense or the added towing capacity is actually needed. More important to get the right gears and that usually means special ordering a pickup.
