Check your engine timing. I was getting 10 MPG from an 88 s-10 4WD and found out the timing was retarded 30 deg. Now I'm getting 17 which still sucks but it's better than 10.

 

Replace Air Filter, fuel filter, 02 sensors, Coolant, Engine Oil, Tranny fluid, diff fluid, transfer case fluid, clean MAF sensor and throttle body, and repack your wheel bearings....should be good to go.

 

You said that you were getting 18-20 MPG's, just out of curiosity, was that before the big heavy 22's? BIgger the rim, more weight and bigger the tire less MPG's.

My 02 only gets 15 MPG (combined driving) regardless if Im driving like a grandma or like I just stole it. I just changed the fuel filter today and am pretty sure my fuel pump is going so that will be next. Its been having troubles while trying to start and last night I turned it on and off about 5 times and could not hear the fuel pump at all, but today it started and I could hear it. I bought a new Delphi fuel pump and for anyone that is in need of replacing one sit done before you read this, fuel pump and filter $394.00. I almost fell out of my chair when he tole me 369 for a pump. My 150lph holley pumpin my mustang was cheaper by 100 and something, so good luck to everyone who experiences some problems.

 

I just did a lil combined run of about 100 miles.... got 23.xx miles per gallon... thats mostly two lane highway and small po dunk towns where the speed limit is 30ish...