changed 8.75-323 to 8.75-355 now speedometer off
 

i have 73 duster 904 auto it had 8.75-323 open end and i changed to 8.75-355 suregrip and now speedometer is whaco, could someone tell me what color stem gear i guess its called to put in trans, it has 14" tires? thanks tire height is 24"

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

speedo calculation
 

im just jumping in because i see no other replies. i think a little math would work. i may be way off, but i hope this will get you started. going to a 3.55 should make the speedo think the car is going slower than it is. stop me if this is wrong. divide 3.23 by 3.55. equals .9. multiply .9 times the number of teeth on you speedo gear (at tranny) and this should give the number of teeth you want. check listing of gears by color for number of teeth. good luck and i hope i didnt send you the wrong direction.
fifthcrunch

No, the speed will read faster than the car is going