Gps's are fairly acurate pending the roads and sat reception, my boat ran 72 on lazer and my s10 which i run at the track and have gotten tickets with and the cops radar was dead on with my speedo all confirm mine is good in south florida. I know every honda that i have checked is 10% off though thanks for checking the fury, now i have to keep it at the speed limit and not think ok im on a honda can go 5 over. Depending on the year of your jeep you could probably change the speedo gear in the tailshaft of the trans to correct it ($25 bucks i think for parts) or if you have a programmer on it can correct it that way usually