In March of 2012, the Texas Mile record was 255 mph, but the GT ran 257.7mph and took the Texas Mile Record.
In October 2012, it bettered the record and ran 263.3 mph.
In March of 2013, it went faster and hit 267.6mph, but came back in October of 2013 and ran what stood for a couple of years at the speed of 278.8mph.
At the higher speeds (260+), Patrick, the driver of the GT, commented that on the 4-5 shift the car would get a bit upset. This was due to the nose dropping and lifting again when he got back on the power. With the shock data from the Motec and the help of Scott Ahlman, they figured out that the suspension was bottomed out from the down force and that was causing the issue.