Recreational Vehicle Lpg Tank Valve/gauge problems of the 2004 Infiniti FX35

The gas gauge is always wrong. Since I first had it, the behavior of this component has never shown full, and shows empty far too early, often 6-8 gallons before the tank is out. I looked up my recall for my airbags, which this car has, and I noticed a number of complaints here. I searched Infiniti forums and found a large number of complaints with recommended fixes. I cleaned the parts, and it improved, but now the gauge is off again, and this isn't safe, since I cannot trust when I will run out of gas. I also wonder about my odometer and what its reading. There seems to be something wrong with these indicators.