01 blazer

The gas gauge is very erratic especially below 1/2 tank. I found a stud on the under hood fuse and relay box that has a strap on it with no nut. Could this be a ground and really need a nut on it? and could this help the gauges especially the gas gauge?

The stud under the hood is not related to the gauge issue. The erratic fuel gauge is most likely a poor ground at the frame near the fuel tank, a poor connection at the fuel pump module, or the fuel level sender is failing. The level sender can be serviced separately after removing the fuel tank and fuel pump module. Life expectancy of the fuel pump is usually somewhere in the 100,000 mile range... something to consider. A complete fuel pump module comes with the fuel pump and fuel level sender. If you decide to go that route, seriously consider AC Delco. The longevity of aftermarket pumps is not good.

already replaced pump and gauge module at chevy dealer with ac version. Gauge is still very erratic. Put a nut on the stud and the gauge seems to be working properly now

Interesting, was the strap a wire with an eyelet or a metal piece on the fuse box? Glad you got her fixed, good job!