I just got back from the driveshaft shop to measure for my new shaft, and we started talking about the speedometer being so far off. My Blazer is an 89' with factory 31" tires, and 2.73 gears. I now have 35" tires, and 3.73 gears. The driveline guy did some figuring, and said I could go to the Chevy House and ask for a speedo gear for a 3.55 rear end, and it should be almost on. Any thoughts on this? Wouldnt they need my original gear to know how many teeth I have, or do I just get one for the 3.55 rear?