have a 96 Chevy C 2500 the tachometer, speedometer, oil gauge, and amp all quit

CK WITH NAPA AND REPLACE ENTIRE ASSM. APPROX COST 300.00

There isn't a common cause with what you stated as the problem. The speedometer, the tach and the PRNDL display share the same power feed. The oil gauge, amp....and the fuel gauge share the same power feed. Nothing points to one feed or the other. You'll have to remove the instrument cluster and back probe the wires in the connector with a multimeter to confirm a bad instrument cluster based on voltage readings. If you reply with an email address I can send you the diagram. Assuming this is the 5.7L engine?