I have a 2000 Nissan Frontier truck and it doenst get good gas mileage. It only gets like 16 city and 19highway! So I am thinking about getting a second gas tank put in, or replacing the old gas tank thats in it right now with a bigger gas tank. My gas tank that i have holds 19gallons right now. What do you think I should do? Get a second gas tank? or should i replace the old gas tank with a bigger gas tank? Also how much does it cost to do either of them?