Shaking accelration and deceleration

Jonesmeister1

Hey all, 2011 G37s six speed. Recently I’ve been noticing when moderately to heavily accelerating in lower rpms, my car will thud and shake once then start to accelerate.
I hit some back roads, over the weekend, and really got a chance to stretch the cars legs. I noticed when in high rpms and letting the car engine break, the car would this and shake as well.

The car was at the dealer last month and with the milticheck inspection, the motor mounts and transmission mount are apparently ok.

I currently have the Z1 poly diff mount. Mods are tune and supporting mods.

Any idea what could be causing this? Could this be a clutch issue? Im just under 90k on factory clutch and flywheel.

Thanks guys!