Yet Another Gas Mileage Question

[Lancialonnie]

Hey Folks, looking for some input on improving gas mileage. I have read through many posts and am envious seeing lots of people getting mid-teens or better MPG. I have restored my 72 C10 long bed with the boards help over these past few years. It is very comfortable and nice to drive, that is until gas in California reached $4/gallon! The original 307 is getting long in the tooth but it runs well. It was rebuild about 25 years ago but very little mileage has been put on it until the last 4-5 years and it is starting to drink a little oil. I have installed an HEI distro, headers/dual exhaust, FITech system w/rear tank and in tank pump, early style 700r4 tranny and a tonneu cover. Every time I added some upgrade I noticed an improvement in drivability and the gas mileage has improved from where I started but I am still only averaging 9 MPG! Is there anything I am missing or is it time to get a 350 crate motor? I am tempted to do it now but this engine is running really well, adding the FI and an OD tranny just made this truck come to life it is enjoyable to drive now especially compared to how it was stock. Thanks for any input!