99 % of the time I get 200 plus miles towing my 5er at 70 mph out of my 26 gallon tank. As was mentioned above I too like to stop every couple of hours anyway so I am not unhappy with my tank size. I agree that a bigger tank would be better but not necessary for me. It would be nice if the fuel gauge reflected the tank level better-it shows empty with at least 6-7 gallons still in the tank. So I just drive to empty and then fill up. The computer does accurately tell me fuel used.
I do carry a 5 gallon can in the back with diesel but have not needed it in the 9 years I have had this truck. I carry it just like I carry chains for insurance. I have needed the chains 3 times in summer mud.