I would agree with the other guy and say that it is in the tranny area, I would look at the torque converter and make sure its locking up in the right gear. I had the same problem in my Mustang with the Ford od I had the wrong set up and it was not locking up properly and it was shuddering like crazy, I thought the car was going to fall apart, once I got it set up properly it ran 11s in the qtr and the shuddering was gone. Hope this helps out.