Dynamometer Results & Comparisons - Input on Dastek Dyno?

Ok, so I got my '00 Trans Am 3 months ago and i wanted to get a baseline dyno run before i started modding it. A shop here on Long Island that my family's shop does business has a Dastek loading dyno that they bought off The Racer's Group (now TRG) like 2 years. Since we're in the process of building a GT3 Cup car for them the owner comp'd me a few dyno pulls. Now as far as i can tell my engine is stock. No bolt ons, stock heads, stock intake etc. My average runs were about 450bhp. I tell the guy somethings up with his dyno and that its just about physically impossible for it to be reading that high. He says he's never had a reading deviate from the the norm on a stock car before, and the only problem he ever has is low readings when theres some tire slippage. I wasn't gonna argue since the guy was doing me a favor to begin with. So I wanted to know if anyone on here has any personal experiance with a Dastek, and if the numbers are really that overinflated or if this dyno just gone bad or what. Regardless I'm bringing it to another shop in like 2 weeks to get a second opinion.