[Big Dave]

I have a P71 Interceptor.

MPG ideas:
Manual conversions are easy to come by for Crown Vics.
If you just have to have an automatic, there is a shop in SC that will transplant in a 6 or 10 speed auto. $$$

Car has 3.27 gears. 2.73 would be practical.
It also has the police high stall (`2200 RPM) torque converter. A 1600 RPM stall would give better MPG and not be such an annoyance to park.

There is CNG in my Vic's future. It's cheap around here.

I put Mooneye (Bonneville-style) hubcaps in it.
I'm looking at skirts for the rear wheel arches.

This vehicle might benefit from a low trunk spoiler.