I've never had better than about 18 MPG, on the interstate i get about 16-17. my machine is a 82 k5, with 31's and 3.42s 700r4 . i used to have a 84 an that thing never got worse than 20. i drive pretty conservative most of the time. I have checked all the things the diesel page says to check including replacing both fuel filters, air filter. lift pump. different fuels. My truck SEEMS to have pretty good power, but i can't drive much over 75 all the time. tranny is not slipping. whats the next step? keep driving and ignore it? any ideas? compression test? POP Test?