Shaking tail of Miramar

I have some problems with Miramar, when i press full accelerator tail of car is amzingly shaking, imho: it's all becouse of insufficient stiffness of car's structure. Sory that i can't record it, just try to do it by yourself, and you'll see. Especially it happens when i install more powerfull engine.

 

It´s a small light vehicle with rear leaf spring suspension what do you expect?

 

I expect that it will making small jumps, not shaking with body flexing.