I found that it is referred to as Aircraft Quality Steel, Milspec 4130 and ASTM 4130. I see where the Winston Cup, Busch Grand Nationals and Craftsman Series Truck use it for their swaybars and Stillen Racing among others use this particular steel for swaybars. It's very interesting!
If anyone wants to research it, it's quite easy using "4130 steel swaybars" or the like on one of the search engines.
Now it kinda makes me wonder why all aftermarket swaybars aren't made from 4130 steel if that's what the big boys use!