I am not sure. When I look at the import racing pages I see many guys who have switched over. Antigravity makes lithium with an equivalent CCA of 1000, so I don't think that it is the reason. I also have seen a couple guys rig up there own in parallel for the street, and saw another guy purchase an antigravity for the street, but it was expensive. It took out 35lbs out of the nose of his car though.
I know this technology for cars is fairly recent, so perhaps the Trans am Tech, may not allow it yet?