Ok, it's a GMC 2500HD but I hope you all can give me some help.

I bought the truck as a project because the trans was stuck in 2nd; got a good price. Fixed trans, then had to replace brake lines, exhaust, etc etc making me think the 177K miles on the odometer is off.

Problem is that the instruments started dancing a few months ago. Tach and speedo would bounce up and down but engine/speed didn't change. Other instruments sometimes joined in. I had to drive it for a while (trying to troubleshoot and see when it was doing it) but then it stopped. ?????

Now it's in the shop because something came loose and is hitting the fan and it started running rough/ no power so mechanic will scan and solve those problems (hope hope hope) but I'd still like know what the gauges were dancing.

I'm fixing to sell the truck and downsize to a Colorado so I'd like to be able to sell it as a good running truck without reservations.

Any ideas???

 

Pull the instrument cluster, and check connections.