An assosciate of mine has derived a device for faking out an engine on low boost, creating more low end HP. We have tested in 25 trucks independantly. The average was a gain of .5 MPG for not much in parts. So far no truck manufacturers are interested in buying the patent. Not even an offer. Sometimes they like to "act" like they are making progress, but most of the time they just cut performance for emissions...

 

The best way to get better mpg is to get low roll resistance
tires and keep them aired up.(No off road tires sorry).

Take off all roof racks when not in use, and slow down just
a little.

This goes hand in hand withkeeping your Disco maintained.

Try not to use Ethanol fuel as it has less power and you will
get less mpgs with it, some of us have to use it do to
where we live.

I saw many things back in the early 80's when you could only
buy 10 gals of fuel at a time most where B.S. the thing that
came out that worked was what we call a cat back system.

The thing that we can do is just plan our trips.