Freeway speeds even things out between cars.

Constant acceleration and stopping in town shows how much fuel a car needs to get moving. A yaris and a Bonne are both fighting the wind resistance @ 75mph, but when going light to light in town, the yaris doesn't have as much to get moving.

Every newer vehicle I have bought progressively got worse gas mileage. It'* really odd. haha. These are the averages I had with each vehicle.

88 LeSabre. 29 MPG average.
97 Supercharged Riviera: 27 MPG average.
01 3.5 Aurora: 26 Average
05 Cadillac CTS: 22 Average!!

I think manufacturers are focusing in the wrong areas to get mileage out of the cars honestly. While you guys are talking about how great a 3800 does on the freeway stock, do you know how much better they do with 30 minutes worth of tuning? I understand spending more time on the computer to "fine tune" the cars better might not be beneficial to them, but if they can improve the MPG on their cars by another 5mpg on the freeway, it seems like they would sell them a lot better.

My GP with XPZ cam, heads, headers, 2.55 pulley, 3.29 gears, intercooler, etc... averages 33mpg on the freeway at a 70mph cruise. Thats with a tiny supercharger pulley that robs a lot of power spinning that thing and a pretty large cam, and at that speed its spinning ~2300rpm IIRC with the 3.29 gears. While I did add some timing at cruise and lean it out a bit, it doesn't ever show even a hint of knock, so I figure a few more degrees of timing and a little leaner and I could easily get over 35mpg with it, I'm thinking 37-38mpg would be possible.

I took a stock L36, leaned out the fueling just a little bit (took it to 15.2:1 at cruising instead of 14.7) and added 5 degrees of timing just to start with to see what kind of gains I would get. At a 72mph cruise from Lima, OH to Holt, MI (~190 miles) I averaged 37mpg. Again in a GP with 3.29 gears. Thats on 87 octane! With some more fine tuning I don't see why 40mpg would be hard to get out of it, and if I tuned it for 93 octane it would probably be able to get mid 40'*. With like a 50/50 mix of highway/city driving this setup sees about 27mpg overall. Do much better than that in your economy 4 cylinder and I'll be impressed.

Thats why I'll be running 3800 powered cars for a long time. Can't really beat the mileage, especially for the power they make, and the other obvious reliability and easiness to work on.