With my 245 75 16s on I'm now looking at a 12.4% difference in my speedo.  Anyone out there figured out the fix for this type of thing?  I saw some threads on a Yellow Box device, but saw that it was causing some error codes?  Sounds like our trucks have more than one speed sensor, and throws codes when they don't match up. 

I Talked to some Suzuki dealerships, and managed to find only one guy who sounded like he knew what he was talking about.  He told me that the speedo can't be reprogrammed by the dealer because there is no variable relating to ring and pinion gearing that would change the perceived speed.

Thanks in advance to anyone with info.  If this can't be fixed, I'll just have to keep doin' the math while driving

Dave

The Yellow box is the only thing I've found to fix the speed-o with.  It can be used but not it the normal spot on the trans as their are two sensors. I think it neeed to be installed after the ecu where it send the signal to the speed-o it's self. I will look and see if I can find find out where to install it. 
George

In my FSM, there is only one speed sensor, and it splits two ways; one to the TCM and the other straight to the instrument panel.  The wire is coloured Blue/Yellow stripe.  Provided the fudge box is inserted after the split to the TCM, and doesn't send any interference back to it, there should be no problem.

Its pretty crude but if you had no other option you could always bump the needle a few clicks higher to be accurate at your preferred cruising speed. When driving slower it would be reading high and vice versa.