Typically these are independent gauges. Fuel gauge can be tested by grounding the sense terminal, should read full. Open it and should read empty. Typically the sensor in the fuel tank is bad. Trim gauge is probably the sender on the side of the drive has broken wires. Tach is probably faulty, on the back is a cylinder select knob, insert a small screw driver and turn it back and forth a few times then leave it on the correct setting for your engine and see if this helps.
1997 2400 SCR
5.7 Vortec / Bravo 2