Firstly, let me say that if you EVER sell your car, PLEASE put it on here as I can guarantee there would be several people very interested in a 4 motion (including me)!!
As for the fuel gauge, do you have an onboard fuel computer? When you fill up does it register 300+ mile range, and as you drive does the range drop appropriately? I don't know whether the fuel computer works off a different sender, but at least it may prove whether the gauge is poorly or not.