I would agree that it is acting like a dog on a chain, either shock, spring or something in the suspension is running out of travel before the launch has used up the energy. Just like a running dog that reaches the end of its chain. Don't forget to look at things like tight ball joints and control arm bushings.
And it is a really neat looking car, I guess it is based on the A body mopar, like we had in the USA, just built in South America ?