[Wanderer]

Your, best bet is getting back to basics. I have not been duped into gas saving accessories, but have found two modifications that have increased mileage

(1) Changing to Mobil 1 was worth maybe 1/2 mpg, switching to 5w20 over 5w30 quieted (not eliminated ) the hemi tick.
(2) Increasing the psi in the tires is good for at least a full mpg. The ride is not bad on the regular cab running 44 in the front and 40 in the rear on the 265/70x17. There 140 inch wheel trucks will ride even better.

The above mpg calculations of actual, not the computer. My computer is high by approximately .5 to .8 mpg. Additionally, the cold weather in the northeast cuts about 2 mpgs on short trips.