Try to reset your transmitter settings and limit the punch with your ESCs current limiter or throttle curve options. I'm not using a Mamba, but these settings should be available on any ESC today.
Hope that helps!

By the way, several guys from local clubs (including me) have experienced a weird response from their cars using a DX3S radio - it just didn't feel connected. Maybe you should borrow and test a different radio just to be sure.
It does not seem to be a general Spektrum problem, as the old DX3.0 worked fine.