Phil,
It is NOT 20% improvement. I regularly got 9 mpg. Now I'm getting between 10 and 11 *if* I drive 49 mph. (not lie-o-meter, real measurements)
I do have air tabs--but never noted any difference in mileage, except with a tail wind--where they lowered fuel consumption a bit (measured by a lie-o-meter). They helped with cross winds--and large trucks. They helped with noise levels in the cab.
However today I was for some time driving 75 mph. The lie-o-meter was reading about 5.2. At 70 that was 5.8 and at 65 6.4. about 1/2 the trip was at 65 mph.
There was a head wind but not much of one.
I drove 585 miles and consumed 77 US gallons. That works out to 7.59 mpg. My RV weighs 13750 lbs.
