I have a 2004 Suburban that has a speedometer that seems to gain speed. I can be going 60 & it will climb all the way to the peg.I can get it to reset to zero by turning the ke to a point that almost turns the engine over multiple times. Each time I hit it, the needle will retreat downward a few MPH. I’m really confused.Anyone have any ideas ?

just use the mile markers and a stopwatch,no need for fancy gizmos,just be safe and turn your cell phone off.

blue light special in automotive,speedos 2 for 300.00 .

or the VSS,IGN SW,BROKEN WIRE,but dont pull codes or anything,like watch the data stream on a real scan tool.

eyes rolling to the back of my head.