This is in my new Cobra which is replacing my old Cobra which we now call "the suitcase" ever since someone crashed into it and turning it into an organ donor.

Anyway, I just got this car yesturday (Friday) but I didn't notice the problem until today. It seems to be basically accurate, only it varies 3-5 MPH.

Details:
1996 Supercharged Cobra
Only 10,000 miles, but driven at the track
4:10 gears
It has had electrical work: clifford alarm (which is disconnected right now) and stereo modifications

All the other guages seem to be functioning properly. What could it be?

I was about to put my organ donor's cluster on ebay, but now I'm holding off just in case. I've never had this problem before.

 

switch the clusters and see what happens.