My 2003 TB EXT LT had a cracked gas tank. The crack was where the filler neck meets the tank body. The check engine light kept coming on just like it would if the gas cap was loose. Take yours back to the dealer...
Vehicle is Difficult to Fill with Fuel or Filling Station Pump Shuts Off Before Tank is Full or Fuel Spits Back/Out When Filling Tank (Replace Fuel Tank Filler Upper Pipe and Lower Hose) #04-06-04-003 - (01/12/2004)
Here is your fix,take it to the dealer they will be happy to fix it.