I just got back from a short trip up to WI and found out a problem with the sled I recently purchased. I recently got a 97 mxz 670 and it shows 2500 mi or right around. While riding the sled on a lake I went wide open and hit only 60-70mph. So i got pissed and I rode with the rest of my family and they went first I then passed them and continued gaining speed but my speedometer once agian stayed at the mid 60 range but my brother said when I passed him he was at 80mph and I flew past him. So then we had to figure out for sure and I rode next to my dad even with eachother to see whats happening and as I was with him I showed 30 or so when his showed around 60. On top of this when I reset my odometer I show much lower miles on our ride. This trip the first day was around 100 mine showed 62 miles. It is in MPH not KPH. Any ideas to what could cause this? Thanks for any help.