ls 400 1995, everything is tuned up. Just did a 4443 mile vacation trip and averaged 27.6 for the trip. Best mileage was coming down from Idaho to Texas 31.4 and 33.1 miles per gallon on 2 complete tankfuls. Worst tankful was 23.9 on the trip. I bought gas at the UTE indian casino in Colorado. Must have not been good gas. Now for you purists, this was all regular gas 85 to 90 octane depending on the station. Part of this run was to see if there was a difference in premium gas and it did not make any difference at all. Prices paid were from 3.13 down to 2.68 per gallon on regular gas. Dates were april 28 to may 21st 2010. Several stations had the "may have up to 10% ethanol" signs on the pumps and the mileage did not indicate any problem or advantage to the ethanol. So no help there....