i think i was wrong about the 91 tune being less powerful than the stock tune. i just did a lap around the block here(5 miles) with the 87, diablo and 91 tune. the diablo felt like it had good power but wasnt as sharp as the 91 tune and the 87 wasnt as responsive as the 91 tune or as powerful. its hard to tell the difference between them at cruising speed rpms, you need to be at 4000 and above to really notice the difference. i dont know how it affects my milage yet, but i can tell you i was getting 11.7 mpg at 71 mph on my overhead display. that seems about right as the fuel gauge goes down quite fast! the truck had 3.73 gears from the factory(got the build sheet off this forum) and i believe they still are. i do have a check engine light on for the o2 sensor heater circuit, so that might have something to do with it. i wasnt expecting great milage out of it, but 11-12 hwy is really dissapointing. im going to fill it back up tomorrow and calculate it myself to see what im getting. btw, the anti spin diff is SO MUCH BETTER than an open diff. i can powerslide the truck from a stop with out the inside tire burnout!