I already drive 55. I also keep my heat/AC completely off. I never did either of those things prior to about two months ago. I went from averaging 325 miles to a tank of gas (4 dr sedan) to over 400 miles. I also top off my tank before it hits 1/2. Shop locally, I walk to the store two blocks away rather than drive a 40 mile round trip to (unless there is a really good sale) Safeway. I am hoping to have my car paid off before gas hits $6 per gallon....because that extra $400 per month can just go into my tank.
During the winter, running the heater can slightly improve efficiency of a gasoline or diesel engine by increasing the heat rate. Very different from the A/C which adds load with the compressor. The fan is negligible compared to improved heat rejection.
You live in a state where one can get away with that.
I don't see people in Fairbanks going without heat, or people in Houston without A/C...
Turning off your AC only saves gas if you drive with your windows up. If you need to roll them down, the extra drag uses more energy than the AC (at least at highway speeds — even 55).