you could try what I have been trying for the last 2 tanks. Slowing down about 5 MPH on average, shifting sooner, and keeping RPM's below 2200 for the most part. I normally average about 20.5 - 20.8 MPG, with a combination of highway and city driving. The last tank I got 22.2 MPG, this tank I got 23.03 MPG. I am going to continue this for the next few tanks to get a good average.

Sean

99 XJ Sport 2 Door, 4.0L, 5 speed, all stock. Daily Driver
79 F150 Standard Cab Short Box, 400ci, NP435, NP205, 35" SSRs