Definitely authentic, just the 2005 version, not 2006. The letters and numbers are white, not blue. The only time I believe they wore the ones with the blue letters was the Thanksgiving game against Dallas a few years back.
Nonetheless, it's authentic. Double stitched, spandex sides, cuffs, and color. And a "On Field" Reebok tag. Nice deal, although I would have gotten the white lettered ones.