3.55 and 3.73 error?

With the 23 tooth gear, I heard that the 3.73's will only be about 5mph off at a high speed

95, you know you can get a gear that goes behind the speedometer to calibrate it correctly for the gears you put in. They're not very expensive either. Since that is the case, I would go for the 3.73's, just because the 3.55's won't give you very much pull over what you already have, which I'm guessing is 3.27's? Anyway, hope this was helpful.

To get a 3.73 to be dead on, you can do two things. First is to pull the tailshaft on the trans and put in a yellow 7 tooth driven gear, and a 21 tooth drive gear. This will get the speedo dead accurate. I did this and when my speedometer reads 80, I'm going 79.66 - close enough for me. The other thing you could do is buy a speedometer calibrater from www.dallasmustang.com. I've heard good things about this. It will get your speedometer dead accurate at a much higher price. Some argue that it is more convenient if you decide to change tire/wheel size. That decision is yours.

Joe