VandykeT/A

A guy I know has a 6.0 GTO, its got a pretty good sized cam and bolt ons. I know hes still running the stock airplane gears still. After the cam he dynoed 428rwhp but before the cam I ran him in my camaro and my only mods were 4.10s, headers and ory, lid, and a programmer. We went from a 20 mph roll in 1st gear and I immediately pulled 1 1/2 cars and held it until I let off at around 115 i guess. I always thought the 6.0s were alot faster than the Fbodys? Was something up with his car?