When I got my truck I was getting 17-18 mpg 15.1 1/4 mile,3.42 gears-Then I added the UPD I took the truck to Ohio pulling a loaded Uhaul I got 18-19, on the way back I got 22mpg 3.42 gears with a 1/4 mile of 14.7.
Then I added the programer hppIII,Pulley,Magnaflow muffler then I drove to Alabama,Florida,then back to the Houston area I got an average 23.5 mpg with 3.42 gears with a 1/4 mile 14.520. The UPD is still the best mod for the money.Just my thoughts on the matter.The WidowMaker02 <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> Keep on Trucken

 

I get 20MPG easy on the highway. 25 if I stay under 60mph. 3.42 diff

 

3rd tank refill, on the 5.3 no difference between stock and UPD, but by sotp it breaths alot easier. I am starting to feel that I will not get the full advantage of the UPD till I change the exhaust.

 

conculsion: UPD dosn't change your gas mileage. This is after 5 fill ups on a 5.3 with 3.73's and a 4.8 with 3.42 (combination city/highway). When I take either on a long trip, I will report the outcome(I have a feeling that is where the UPD will start to make a difference)