well i think my odometer is just really off. I drove from town to my house and filled up my truck(it's 20miles) and it used 1.41gallons of gas, i'm so happy now. but i did buy a fuel filter, air filter and a PCV valve. so maybe 13.5 after that and 15 after i fixk the plenum gasket

 

It's hard to get a correct reading from the miles that you drove. Try going through an entire tank and then check the mileage. I think you will get a better reading!

 

I've got the dual tanks, and I can get a shade over 400 miles out of 27 gallons if I stick on the highway. That's a rough statement, but my MPG ultimately averages out to 15-16 on the highway. The technical stats for my truck are in my profile. What's yours like?