Just wanted to post an update. I got my Superchips tuner Friday and of course had to play with my new toy. When I got to the part where it asks if I want to change tire size and I said yes, it showed 28" as a starting point. Now I'm not sure if that was just a generic number in there, or if that's what it read the OEM was from my stock program. Anyway I changed that to 31", and used the 87 octane tuning, and am very pleased so far. I think I might have to play with the tire size though because on the expressway this morning it seemed like I was going slower than expected. I'll have someone set there cruise at 70 and follow them to compare though first. The truck drives and shifts much smoother now. I switched in the middle of fill-ups, but already noticed some change in mileage. I've been getting 13.5-14 mpg since November with combined highway/city. Just filled up this morning and got 15.37, and that was more city than normal. Will update again with next fill up.

 

correcting the speedo (and in turn the odometer) would make that much difference because now your showing more miles traveled