Big Ugly is, as the sig shows, a '86 Chevy K30 M1008 CUCV. 6.2L diesel, TH400, NP208, 4.56 gears, and originally it had some itsy bitsy tires that MIGHT have been 31" tall. The military wanted them to tow and haul, not go fast. Now it's got some 36" HMMWV tires on it and the speedo is over 10% off. I've checked with my GPS and it's somewhere around 13%. How's a guy supposed to fix this? I know I have a speedo cable and a speedo gear in the transfer case...different speedo gear? Never had to do this on an older GM before.