coil-on-plug affecting mpg after 55K?

[morsecp]

I have a 2007 sebring but I assume this would apply to any engine with the world 2.4 in it. This car has the "new" coil-on-plug design.

Ther service notes in the back of the owners manual say that the plugs need changing at 30K but my dealer says not to, and did not at the 30K service.

I have started noticeing a fuel economy drop now, I have tried the usal air filters, tire pressure.. but I can't seem to get the highway fuel millage back up to where it was at 30K miles. I am getting 28-29 mpg at 55K where I was geting 30-32 at 30K miles. I am driving the same 54 mile commute in the early am so the driving is smooth and constant with the cruise on. So I doubt its a driving style change.

Does anyone know if chaging the coil-on-plug(s) would fix this? Or should I look elsewhere.