I bought a DiabloSport Predator thinking it would do the tire size change but it only does that on the 06 and up. Mileage is also a factor. The truck had been getting about 17 to 17.5 mpg with the Diablo Predator my mileage is now 21.5 to 22.3 I have changed from stock tires to 325/70/17 (about 33.5in tall) speedometer off by about 8 mph. I have to have a programmer that will let me correct my speedometer. I love the power & mpg gains from the predator. Would like some input on what my options are.

 

the smarty and bully dog do it or, if you're just looking to change tires size without performance I believe superlift and BD sell speed calibrators.

 

I got an idea for ya.
Superlift makes a speedo recalibrator for when you change tire sixe.
There like 195.00at summit
Hope this helps.

 

You may not like going to a dealer, but you could get them to do it by the revs per mile. It seems like it would be cheaper than buying a programmer. For my customers I do it for free...

 

Supposedly your goin 66.3 at 60 or 33 at 30 on the speedo got that from http://www.miata.net/garage/tirecalc.html
I used them when I tossed on 34s and just drove according worked for me if ya wanna save some coins for a while, I was just saving so I could get into a cummins apparently it paid off!