GMC SIERRA INSTRUMENT CLUSTER GAUGES TACHOMETER NOT WORKING

My Speedometer Gauge Bounces Up And Down Periodically And Most Of The Time Reads Max Speed. I’m Not Sure If This Is Normal But My Rpm...

I Have A 1995 Gmc 2500 With A 5.0 L Auto 4x4 When I Start My Truck, Very Frequently The Tach And Speedo Do Not Work At All, I Believe...