Occasional buck/surge/lurch when lifting under boost

[turbo ride]

One more little thing that is going on with my car - as I've mentioned in other threads - I think my WUR tuning is pretty much where it's going to be. Car is running great.

But occasionally when I lift when at WOT and high boost the motor will buck - I would say it is more drastic than a surge or a lurch. I have a brand new bypass valve (note - car is a 964T so a different bypass valve system than the 930's use). I would say it seems to happen when at a high boost and I lift suddenly or quickly, but not so much if I lift slowly.

While in the middle of the tuning process I seem to recall this happening more when it was running richer - so maybe I should go a little leaner?? But maybe I'm way off...

My wastegate was apart recently when fredmeister modified it and he said the diaphragm was good.

Any input appreciated. Thanks!