Hmmm, is it missing, surging, (that's a lean mixture), or vibration?
Sometimes it's hard to tell.
I'd check my engine mount bolts. if they are all tight, loosen them and let the motor,"settle" in the frame and re tighten.
Check ALL the bolts, the rear tire, exhaust, etc to find Something.
If it was the timing, you'd think it'd "ping", be gutless, hard to start.
Here's food for thought, could it be tire balance?
Might just be a "tight" motor protesting being asked to run at that RPM.
Does it do it at THAT RPM, no matter what gear?
RE check you trans lube, (could it be low?).
What did the plug look like?
Keep us posted.
Joe
So many bikes, so few $$