The tach and fuel gauge sound like a ground wire problem.
The running problem sounds like a fuel pump. It too could be a ground problem. Need to check over your grounds, there should be at least 4.
One from battery to engine, will be large batt cable. One from negative post to rad support. One from engine to firewall.Also it should have one from engine or body to the frame, prefferably from the engine to frame, as the fuel pump grounds through the frame.
If all checks out, perform a fuel pump pressure test.
It probably wont have a test port for PSI test, so you will need to rig something up. You also will need a good gauge that reads small pressure, like 20 pounds on at least a 180 degree sweep.The TBI runs about 13 pounds. Using a gauge that reads say 60 pounds wont give an accurate assesment as the scale is too big.Hence the 20 psi range. If the pressure drops to 7 or8 ponds, it wont be easy to tell if the gauge reads a scale that is too large.