Quick Detail and rags is my bird poop weapon of choice . . .
On the gears/mileage question, I recall when buying my 5.0 that posters on this and other sites' forums estimated the difference between 3.31s and 3.73s at 1-2 mpg at highway speed. By the same token the 2.73s might have a similar effect vs. 3.31s, but having driven my 3.31-equipped 5.0 now for awhile, I'd be concerned that 6th gear would be come less usable. Right now, 6th has OK passing power, but you do sometimes need to downshift to 5th if you need to act quickly (4th to suck the headlights out of whatever vehicle you're passing!). That said, 2.73s are standard in the V-6 and people seem to like them, so maybe I am wrong. And with an Automatic, the story might be different.
All I know is one of the reasons I got the V-8 is so I could drive the heck out of it before Big Brother finds a way to outlaw cars like this. No, I don't need a V-8 and 420 hp in the practical sense, but it sure is a heck of a lot of fun, even on the Interstate, and for what it is, I am blown away by the mileage I am getting.