I have an 86 firebird with the 2.8 v6 and an electronic vss. As i'm driving at about 50 mph the speedo reads like 23 mph, at 40 its like 17, at 55 its like 25 on the gauge. I had someone ride in front of me and tell me speeds on the phone to confirm that my gauge is way off. keep in mind everythings stock size including wheels and tires and rear gears. I am trying to troubleshoot why this is happening...the odometer seems to be working properly and that works off the same vss so i dont think thats the problem, and i pulled the gauge and circuit board and everything looks good. I think if the vss was malfunctioning it would set a code. I'm thinking maybe a bad ground but i wouldnt even know where to find it since chilton's manual doesnt help a bit as far as electronics. any help? its kindof a frustrating problem i need to take this to inspection soon...