I may be wrong, but I do not believe that the gauge is bad. More than likely, it is an intermittent electrical connection somewhere else in the system. Intermittent problems are hard to troubleshoot, but you may be able to get to the connections on the back of the gauge with a multimeter, and see if it show erratic readings when the gauge itself is erratic. Then at least, you could rule that out.
USAF 1965-1971; USCG Master
2002 Horizon 36LD - 2000 GMC Sierra 1500 4x4
Indian River, De