Okay I had my tranny rebuilt and when I got it back my spedo goes crazy above 60mph. its at the shop now and Im wondering how the system works like is there something that the shop could've screwed up inside the tranny to affect the vss b/c I know that if they replace my sensor and thats not it there gonna charge me for the part b/c its electrical and they cant take it back? On top of that I drove about 500 miles w/ no dipstick b/c the idiots didnt put 1 back in. So tranny fluid was leaking the entire time and the vss is like an inch away from the dipstick hole and the fluid could've screwed it up. ohh yeah I have an 99Z24 and the tranny is a 5 speed

Usually what happens is some metal shavings in the transmission collect on the speed sensor because it is magnetic and often it will malfunction at high speeds. I assume your speedo will just drop and then bounce back up to the proper speed and sometimes bounce way higher than you are going. Its easy to fix, take a 10mm wrench, jack up your car and the speed sensor is right on top of the trans. Take it out, wipe it off and put it back in, tighten the bolt and you are done.