Well, I got it figured out. It had a 23 that was WAY off. I tried a 22 and it fixed it by 5MPH. Then I tried a 21 and an 18 and it seemed to go the wrong way. Then 20 tooth and BINGO, DEAD ON. It read perfect from 25 to 65. I was amazed how accurate it was. At 70MPH on the speedo, it read by satellite at 72. That was the only real change. And I won't be going that fast or above that speed. I was mainly concerned from 40 to 60. So if you have a M21 - 3:73 and are running Good Year E70/15's, this would be a good starting point for accuracy. Going to check some of my other cars and see what happens. I am shocked GM missed it by that much. But maybe some things changed in thousands of miles? The internal gear was in nice shape. And the 23 tooth I took out was also perfect? Danny
