Gas mileage went down

I used to get 370 miles out of a tank of my 2000 Intrepid ES (3.2L), now it is about 300 miles for the last 3 tanks. My car is 66,000 miles. I haven't done any service maintenance except oil/filter change. Engine RPM has been steady around 7500 with a light vib when idling.

What could possibly go wrong with that mileage? What are your suggestions?

Thanks.

my '96 went like that for awhile and i had to replace the transmission. 7500 rpms seems extremely high to run at considering mine runs at roughly 2000. i would take it in and have it tuned up and see if that helps.

Or... I might have had a brain f*rt. The RPM was 750, not 7500.

But anyway, the RPM has dropped to 500 - 600 and consistent at that level for the past week. I don't know if it's good or bad. Also, the gas mileage also went up, got about 330 miles before the "low fuel" light pops up. I would want to blame it on the weather (it was colder during that anomalous time) but still think it needs some attention.

Thanks.

well here are the typical gas milage fixes....

Air cleaner
Plugs, wires
Oxygen sensor

just some thoughts