im actually not sure but why wud the tanks be different? his truck is one year older than mine
you deffinetaly should have a 19.5 cus you have a supercab and that always has the 19.5 but theres always that slight chance you do have a 16 some how but its very unlikely.
your mileages seem really low. i've put 2k miles on my truck in the past month and never got below 22mpg. the best i've seen out of a full tank was like 25 mpg that was from a tank that got over 400 miles..