I had same problem with sending unit. When I installed new sending unit along with new Auto Meter gauge, it wash way off. When tank was full, gauge showed full. Drive about 50 or 60 miles and gauge would drop off to 3/4, then go another 40 miles and gauge would drop to empty. Go fill the tank and only would take 9 or 10 gal. to fill it up. Now I gave up on trying to get the gauge right after 2 new gauges and 3 new sending units. Now I just set the trip meter to 0 and look for a gas station at 150 miles. Then fill up and reset trip meter.
