taking off from a stop issue

[bucannon]

When i take off from a stop, no faster than average motorist. I notice a slop in the drivetrain. I not only can feel it but hear a noise that i have a hard time describing in text.

My first thought is that is is the transmission cross member. I checked the mounts to the frame and it feels solid. I think I would have checked the bushing too but i cant remember. But were going to assume that i did.

this leaves the rear end, I have 3" lift blocks, stock springs. or the motor mounts, which I believe would be obvious under a rolling takeoff with hard acceleration

what if my cab mount bushings were shot, would that be what im feeling?

what could my issue be?