What's the best gas MPG you have had?

Best I ever got was 29.3 by the computer.  This was going through several passes on I-5 with the cruise set at 70.  Once I got to my destination I ruined it by having a little fun on a back road!

2008 Coupe LS-3  Corsa Extreme Exhaust with Crossover pipe and Vararam Intake System.

I have a 2005 6 speed coupe and the best overall mileage I  racked up on a 800 mile Interstate run was 27.5 when it was four months old. I have not been on any long  trips since.

Greatest per mile gallon figure for a tank: 26.879 (6/11/08) Greatest distance on a tank: 421.0 miles (11/13/2009; 15.918 gallons; 26.448 mpg)

i bought a 2006 coupe with 12000 miles, gas milage best number so far is 21.6mpg on the highway "65mph" the car now has 13300 and 21.6mpg is tops.  do you think something might be wrong with this car? i am the second owner and thought i would be getting much better gas milies right out the gate. any ideas, comments are very welcomed

thanks,
anthony

You fuel injectors may be clogged. Try running Chevron with Techron gasoline and additionally adding some Chevron Techron/Fuel Injecter Cleaner  to your tank. Costco sells it at a discount. I had a 86 that had one injecter completly clogged and that opened it up. Since then I only run Chevron or Shell (has additive). Presently I have a 2001 convert, a 2005 convert both with the Z51 (lower rear end gear ratio) and a 2010 Grand Sport convert. The first two see 25 - 27 mpg but the GS does not do as good, maybe due to the wider body and tires. I bought it in Texas and brought it to CA. At the beginning of the trip I was getting 20 and at the end 23. I was doing 80 mph where I could driving the speed limit plus 5 mph.

Picked up my 07 in Carol Stream Illinois and headed back to North Dakota. Maintained 5mph above the limit all the way to Fargo and got 28.3 mpg with a minimum amount of playing. Once inside North Dakota I played a lot and got 27.5 mpg!

I consistently get 25/26 mpg on my '05 Convertible running between 70-75 mph.  Most folks are amazed at the gas mileage!

Whether you have a manual or automatic transmission also makes a difference.
With the type of driving that I do here on Long Island, I noticed about a 2 to 2.5 mpg difference between my '07 with an automatic transmission and the '08 with the manual transmission (25mpg to over 27 mpg). Other differences are that the '07 had the LS2 engine, and the '08 has the LS3 with the  Z51 manual transmission which has the taller gear ratios (about 10 to 14 percent) in the first four gears.