New 2007 NISMO Frontier shakes bad!!
 

I recently purchased a 2007 Nissan frontier nismo edt. When I am driving 35mph @1250 rpms and start to accelerate the truck starts to shake very violently. ( Almost like I am driving over a brick road) I have taken it to the dealership 3 times and they can not seem to find the problem. Does anyone have any suggestions on what it could be or what I should do?

Thanks