What Walker said. Civilian jeep has a great troubleshooting logic for all the gauges. Read up on it and get busy with your multimeter checking voltages and resistance on the gauge and sender.
WORTH SAYING: Check that your gauge cluster and dash have a good ground, preferably straight to the battery. Also, I ran the tank sending unit ground straight to the rear crossmember with an crimp terminal. I used "oxguard" anti-oxidation on this connections.
So I think I'm getting pretty good at dropping the tank. Did so today from 12:00-12:50 to adjust the float level. I tried and tested but it needed adjusted because after 15 gallons put in it read 1/2, drove it 60 miles or so and it was on E. So I dropped it to adjust, read bend, the arm down so the float "floated" higher across the resistor. I really had no way of knowing how much gas was in there so I measured it. The tank is roughly 13" from bottom to top and I had 4" of gas in it. I took a stab at 1/4+. I'll fill it tomorrow with 5 gallons and check the reading and then say 5 more, etc. and kind of extrapolate what my gauge readings are. There's still not a comfort level running her down to E. Have to say I really do like the hard top being on there!