Did you measure compression and squish after install of the new head? Is this a new head or did you have them machine your existing head?
Do you solely ride at over 5k in elevation?
I wouldn't go with a big bore to solve your problem...
What did you do to dial your jetting? Some solutions work better than others.
What is your gearing? Rear sprocket size.
Which pipe is on your bike?
Maybe an aftermarket pv cover might help.
Jeff
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