Ford - F150 :: 2004 - Exhaust Smell After Plug Change

I have a 2004 f150 LAriat supercab 5.4L triton with 120,000 mile on it. Without good reason, I let the dealer convince me to put new plugs in it. Ever since, I've had a serious smell in the cabin of gasoline and or exhaust, and a 2MPG drop in MPG. At first it smelled like gasoline. I took it back to the dealer and they said a connector had backed off, which is code for I don't even want to know what. They "fixed it" but the smell remained.

They then changed the rings on the fuel injectors. The smell got better, but there is more of an exhaust smell now. I checked many blogs about it and found several bloggers with almost the same exact situation. I suggested to the dealer that they need to check that the proper spark plugs were used and they were correctly seated. They of course confirmed this but God only knows if they actually checked.

I also looked up to see if there is a cabin filter on this vehicle and there seams to be some disagreement on the blogs about this fact as well. Now that the cold weather has arrived, I prefer not to take the cowl off or check the plugs myself until it gets a little warmer. The smell is noticeable most of the time and especially stopped at a light regardless of the heater or air conditioner. Should I be more worried about the smell or the fact that I actually took it to this dealer in the first place?