My old 2005 F150 w/ Triton V8 had a 26 gallon tank. We had to be very cognizant of where the next gas station was when going cross country, especially in the large open spaces in the southwest.
My new truck, 2014 F150 with Eco came with a 36 gallon tank. Makes things more comfortable.
My friend has a Chevy 2500 w/ Duramax diesel, but it came with only a 25 gal tank. He had to stop a lot when towing, but he found an after market gas tank that holds 50+ gallons. It fits underneath the truck. He's a happy camper now. (Pun intended).