Sounds like you have a emissions car with the extra tube next to the filler tube ?
There are three lines,1 is for fuel and the other 2 are for vapor and venting.
If you plug the venting of the tank you will have issues.
Usually you would have a vented gas cap or filler tube.
Sounds like your Charger cap is not vented.
Simple fix is to go to a vented filler tube.
Suprised your car is running at all the way you have it.
California cars came with this emissions package (extra tube in trunk).
I got rid of the tube and went with a vented filler tube and gas cap.
