Wow! I don't have anything that I could tell you that would help, but that is definitley really bad MPG! I have a 97 1500 with almost 300,000 miles on it and I can go around 350 miles on a single tank! Give or take some depending on the speeds and location of course - but wow.
I gained a few mpg from having a tune up, on highway 100 miles in no stop and go traffic burns about a quarter of a tank now.
