Speedometer help.
I need some help with my speedometer. I bought my 2002 gt and it had a v6 speedometer cluster in it. It read right compared to a gps speed and rpm's are right on my livewire tuner. Didnt like the fact that it made it look like a v6 so I bought a gt cluster. Switched the circuit boards so it would work and it reads 10 mph off compared to a gps speed. So the speedo says i am going 50 when i am going 40 as i get to higher speeds it changes a little. The rpms are also about 5000 off compared to the livewire tuner moniter. I wasnt told whether it had upgraded gears or not. I was told by someone that it had a modded motor in it when the kid before me bought it and the kid blew that motor and put a 99 gt motor in it. Kid pretty much almost blew this motor but when I bought it my friend fixed it back to how it should be. Is it possible that I do have upgraded gears in the rear end? Also can I just up the revs per mile on my tuner to fix the problem? If so how many revs/mile? Also if anyone has any idea why someone would put a v6 cluster in a gt? Any help would be appreciated Thanks