Our 99 Quest recently was exibiting poor gas milage as is yours. Then about a week ago there was very poor acceleration to go along with it. After a week at the dealer (Who did a lot of head scratching) the problem was traced to a rust clogged exhaust pipe forward of the catalytic converter. If you start to experience poor exceleration you may have the same problem. Dealer said that the pipe has a sleeve and when it started to rust it slowly constricted the exhaust flow which affected gas milaege and slowly was choking the engine till it robbed power. ($1,100.00 repair, ouch) I hope yours is a simpler problem. Good luck and let us know what you find.
Mark