speedometer gearing

Well, I got my speedo fixed & it seems to work great but also seems a bit off. I believe I have a 3:54 or 3:23rear gear in the truck (it's stock). Anyone know what speedometer gear I need when running a 27in tall tire with either of these gears? Any calculator I find shows I need something like an eleven tooth version but I can't seem to find any with that few teeth.
I'm guessing I'm doing something wrong in the calculations. Any ideas?

try calling these guys tell them what you have..

http://www.aandatrans.com/Departments/Chrysler-727-Trans/Speedometer-Gears.aspx?page=3

see if this helps

http://www.mymopar.com/speedometer.htm

Thanks! I'm sure it will help a bunch!

The page dix recommended is good (I've used it before):
http://www.mymopar.com/speedometer.htm

There are values in between that aren't on that page (tire size and tooth count).  For example, if your tire is exactly 27", you'd want:

3.55: 34 or 35 tooth gear
3.23: 32 tooth gear

Thanks to all! I got it figured out & a 31-tooth gear got me within 2mph of my reading. Since that's good enough for the manufacturers I figured it's good enough for me! Again, thanks to all.........