I have a problem with my speedometer.  After the shop put in my 331 stroker they also put in the correct gear for the speedo and calibrated it.  However I was pulled over yesterday and found out that I was going 10 over what I thought I was going, (which was already 10 over the speed limit.)  A little while ago I took off the dash panel to swap the background and had to take off the speed gauge but I don't know if that would be the problem.  Any opinions of this, like how to fix it?  Thanks.  

You need to go to a shop and have the proper speedo gears in the tranny replaced.  It depends on the year of your speedo. tire height and then they should be able to get the right combo.  If they're pros at it, they should also give you a speedo certificate once they're done, I had mine done at my Ford dealer and it states the year of the car and the tire height for proper calibration.   

i appreciate the help on that, and if u hav anymore pointers, i could use the help bc this is the first mustang i hav owned and i havnt worked on a lot of fords, i have a built 440 that i worked on my 8 years and this car is my new project so thanks for the help