Intermittent low power

06 dsg 160000 mi I bought new all stock.
When accelerating especially for first time after startup it will have low power, makes a rattle like a gasser “spark knock” and won’t shift. If I let completely off and on accelerator quickly it will take off with plenty of power and shift normal. I have searched for hours on forum but haven’t found anything comparable. Any help would be greatly appreciated.

Try this zip tie mod.
It sounds like the turbo's vanes are shutting too far down and choking the the engine out. The chatter is the vanes bouncing as exhaust gets forced past them and they slam shut repeatedly.
This may give you a better sense of what is going on:
https://www.myturbodiesel.com/wiki/turbo-stop-screw-adjustment-tdi-engine-zip-tie-engine-hesitation/
It is an easy thing to try and will allow you to at least rule it out if it does not have any effect.

If that does not work then check your fuel filter for blockage. That will not explain the knocking sound but may be part of the bigger picture.
Both of these symptoms are very common on the BRM Jettas