I finally got around to looking at my build sheet for my 06 4.7 XK limited. Under Standard Equipment it lists a 20.5 gas thank. Ok this is what I thought was normal. Under options it lists "7.5 Additional Gallons of Gas." Does this mean the optional tank is 28 gallons or that they put in an additional 7.5 gallions of gas into the tank at the factory"? Thoughts.