I recently bought a 2006 XLT with 105,000 miles. The fuel gauge only registers 3/4 full when I know it is full. I see where there is an issue with filling it up on some, but I can fill it up with no problem (based on "XXX miles to empty" reading and fuel in the filler neck). I ran the "gauge sweep" test and the gauge needle goes to full. The gauge will drop as I use fuel down to close to empty and give me a warning of low fuel, even though I think I still have 4-5 gallons left. The gauge now shows a little less than 1/2. The rest of the diagnostics says : Fuel level 91, Fuel level % status 90, Inst DTE 138 miles, Fuel on off Z 89 0 100, F#S on / off Z 16 50 50. Any idea what any of that means? What I can gather is that the cluster is working since the sweep looks good. I assume that the fuel pump sender is bad. Is that the correct assumption? If so, can you replace the sending unit or do you have to replace the pump? Thanks for your help.