Biggest way to get better mpg is to adjust the nut behind the steering wheel. Sounds like you are going a constant highway speed. You need to mix it up by slowing down and speeding up to add a P&G cycle to your drive.
Sounds like its at the stock height, have you considered cutting the springs to lower it and reduce air profile?
Have you done a compression test as the engine maybe warn more than it was before.
Have you checked timing, air filter, plugs and such? Have you double checked to see if a wai helps mpg on your longer trips or actually hurts it?
Is the egr clogged up or working of? Has the alignment been checked at some point?
Is the electric fan cycling or running all the time?
All these little things add up.
