Small thug on takeoff seems like transmission mount loose but looks ok.

Its gotta be bad trans mount ,recheck..

There is quite a few possibilities. The only way to find out is have a front inspection by a good shop and have them test drive.

very easy to find out, take it to another mech and have all mounts ck'd out

Bowling ball left in the bed!

I had the same thing on my 2008 silverado with 90800 miles the clunk upon take off from stop it had a broken motor mount on left side. The mounts have a steal strap over the rubber and this is where the clunk comes from it took me about 2 hrs. To change out the mounts cost from $36 to $75 each depending on where you buy your parts