gauges mystery on dashboard

1993 1500 30 TBI has issues with the dash gauages.
Tachometer boucnes slightly, speedo gets to 60 mph when I know I've gotta be doing about 30 or 40 mph. According to my gas gauge, I've had
a full tank of gas for well over a week now. The engine temp stays just above 110 degress no matter how long I drive it. Oil pressure never gets above 30 psi.
Every now and then the gauges will rise to what I think are normal paramaters, but most of the time they're well below or way out of wack from where they should be.
Big problem is that I've got a knocking in the engine and I'm not sure if the oil pressure truly is low, or if the gauge problem is giving me a false reading.
Sounds like a short, right? Trace it and find out what's going on? Anybody seen this before? Oh, I should mention that the ground strap on the back of the engine block is broken. Would that have and affect?
Thanks for your help.
Brian
Thanks
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bad ground or faulty cluster...that would be my guess.

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also try unhooking the cluster and rehook it back up

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