On mine I am having the same or similar challenge getting the needles just right. Initially I could advance the throttle quickly to mid stick and it would go, from Idle to full or mid stick to full there was a lag after prolonged idle. I wouldnt call it a stumble but it didnt take throttle. So I have the low speed to a point where I think its lean enough, then started working the high speed lean in 1/16 turn increment and seeing improvement in throttle response.

But my initial behavior was similar to yours, that is its fine in the pits but on the take off roll it didnt take throttle for a good part of the takeoff roll but finally goes. I also see the oil spots on the bottom of the plane, Im at 32:1 pennzoil.

Where are your temp probes located?

Just a side note for anyone, once a plug is established as rich, that is its dark, when you get the needle set lean does it go ahead and lighten up?

Brian