I have a 2002 Jeep Grd Cherokee 4.0 liter. I keep getting codes: PO442 Evaporative Emission Control Leak Detected (Small Leak) & PO455 same as above but Gross Leak. Dealer keeps telling me it's a bad gas cap but after the third one I think I need to go to a different dealer. Does anyone know what this code means?

Is the cap you're using factory or aftermarket? Tiny differences can make cheaper caps not fit right. Also check where the cap seats for anything that could prevent a good seal. They've told you the codes that are setting but have they diagnosed the car? The leak could be at charcoal canister or the lines going to/from it... Good luck!