speedo accuracy

I would like to fix my speedo accuracy. I have an '85 K10, Sm465 trans, 32-11.50, R 15 tires. The speedo is about 5mph slow at 60mph. Is there something out there that will allow me to calibrate this? Thanks again for the help guys.

yeah, here's a few links.
you'll need to know your total tire diameter, find it by measuring from the ground to the center of the axle. multiply by 2.
this is your total diameter, not the same as rim diameter.
you'll also want to know the color of the 'drive' gear in the transmission tailshaft. you then order a driven gear with the correct number of teeth to fix the inaccuracy.
you could also do what i did.
get an electronic drive speedometer and a hall-effect speedo sender.
the hall-effect sender will convert mechanical rotation into a digital signal, and installs right behind the dash.
then you calibrate the speedometer
hold the button, drive a measured 2 miles, push again.
done.
without taking apart the tranny.
you can get the electrical sender from some tranny shops, or summit racing
here's some sites.
http://www.transmissioncenter.net/
http://www.tciauto.com/Products/TechInfo/speedo_gears.asp
http://www.speedometershop.com/ratio.html#ADAPT
good luck.