I had the similar issue: gas gauge stuck at 1/2 full. The fix was to remove tank solenoid, remove float mechanism from tube and CLEAN (with sandpaper) central shaft which float moves up/down, spray some wD40, and put back together. Just be careful not to brake any of the wires. Also, you should measure the Resistance (K ohms) at:
Empty-67K ohms
1/2 Tank - 35K ohms
Full Tank - 5K ohms
pics shows Resistance at Empty, Half, Empty
Gas gauge now works. shows 3/4 full
