Just recently my speedometer has started jumping around. If im going 45, it will bounce back and forth between 35 and 55. Sometimes when i start out it wont start moving untill i get to about 35 then it will jump up real quick. It never did this before. I did just recently get a new stereo and speakers installed dont know if that would make any difference. What could be causing this??? Its really annoying.

 

This sounds like a binding cable, but your 91 should have an electronic speedo. Perhaps some wires were disturbed when the stereo was installed.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

your ar is just telling you it wants to go faster, listen to it.