speedometer is way off and i have stock steelies on it. i know im going 70 and it tells me 80 it's off 10 to 15 mph. what do i do?

 

ttt

 

try a different VSS

 

borrow a gps, see how far it is out, remove the gauges and front glass, gently pry off the speedo needle with two flat screwdrivers, be carefull, place it in the correct place, gently push a bit, not all the way on, you may need to move it again, when you get it right, reassemble the gauge cluster.
It's easy.