[brucepick]

Does this men your car used 1.55 gph at 2700 rpm, not moving, warmed up, with all accessories switched off? I think that's what you're saying.

If so, try this calculation. Turn the math around and divide gallons by miles. That will tell you how much fuel is being consumed per distance, JUST to keep the engine turning. That is, not considering any useful output from it.

Now compare that number to your actual usual gallons per mile at that cruising speed. For my car, I found a surprisingly high percentage of fuel was used just to spin the mechanicals.

Now, if only you could cover distance without rotating your engine quite so many times. You'd save all that fuel.

Voila. The reason why many of us are big fans of coasting, with the engine idling in neutral or off as appropriate. Every revolution of the engine eliminated is fuel saved. You're better off at 2/3 or 3/4 throttle part time and engine "on vacation" the rest of the time, than you would be driving in a reasonable gear at whatever throttle position would work at that speed.

Using that technique, your terminal mpg isn't terminal at all because you can cover distance on highly reduced fuel use or none at all.