For perspective, on a 1100 mile trip, I was at around 27.5mpg with 3 adult passengers (total adult 4 occupants) and a full cargo bay with an SS (5 speed/stage kit).

How about next time, you give me the Vette and I'll leave the family and baggage home?
I could use the 1mpg gain

 

I got ~28 MPG over the winter.
I think most of the drop was doing short runs to the store, DDs, Blockbuster then back home to hibernate until we ran out of $hit again.
Those short runs don't get it warmed up enough.

This past week I've taken a 360 mile round trip to Northern Vermont and another 180 to Keene, NH.
Add in a few longer local trips and 50+ degree weather and I'm getting about 32 MPG over a tank and a half by playing nice

 

I average 26 MPG a lot of city driving and bumper to bumper SOCAL Freeways

 

Aerodynamics allow the Vette to overachieve. I would agree with your premise that a late model 3100 lb 4-cyl should get better mileage. Most vehicles improve with time due to more conscientious Driving, loosening drive train, and/or finding the most efficient fuel. The 2.2L I'm driving with 34,000 miles is getting 30 MPG.

 

My 2010 1LT 2.2 auto 1200 miles has been averaging 26mpg in town and 34mpg on the highway. Great ride, great economy! Don't beat your car and you can do this too.

 

I average between 18.5 and 22.5 in city, highway(with cruise set) is around 28-29 I am still under 7k miles, and that is 5-12mph over the speed limit. 2.2L Auto. No engine mods done so far.

 

I believe your mileage will further improve as it hits around 10K

 

Our 2.4 auto has none of the tricks other than a regular maintenance schedule the wife absolutely clings to and Nokian WR's for skins (always) with 28-30mpg being the norm travelling the Trans Canada at 72mph.

 

I'm on the road and my last two tankfuls I covered 501 and 510 miles in my 2.4L auto. I drove down to 45 miles range in the first tank and 85 miles for the second tank. It was most all highway with my averge speed being 55 mph or so. I hit 67,000 miles. When refilling I did pump in over 15 gallons of e-10. I hade an initial fill up when I left Florida of no ehthanol gas ($3.199/gallon @ 90 octane) and saw no real mpg gains. It wasn't worth the $0.60 premium price per gallon.

 

As far as I can tell it mostly has to do with how you drive. I just got back from a nearly 1500 mile trip a couple of days ago. It still says over 36 mpg. I saw over 45 for a while. But I tend to drive like an old lady on ludes.