Won't Rev past 4k


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I recently had a 750 build done by R&D and since I've got it back it won't rev past 3700-4000 RPM. It starts cutting out at that RPM then when you roll on the throttle all the way it's like I hit the kill switch.
Things I've checked/done:
Compression 224 left 226 right
Valve clearance .006IN .008EX
Brand new 34mm mikuni from Hoos racing synced and jetted from one extreme to the other changing needles, needle jets, ran it with and without air jets. No change other than rich/lean conditions.
Brand new Electrex world ignition degreed to 35° BTDC. Have gone from 28°-38° BTDC with no change either way. Timing light shows I'm firing right where I set timing and never loose spark at 4kRPM from what I can tell.
Thought it was a tooth off on mechanical timing so I pulled engine and valve cover to check it and it was within 1° of cam specs. 250-30 mega cycle cam.
I wasn't billed for springs, so I pulled springs and checked springs rate and I was 20% low on spring rate. I ordered the correct springs thinking they were floating. Assembled, and installed engine back into frame still no change.
2 into 1 exhaust to obstructions. Running C10 VP fuel. I removed kill switch to eliminate that. No other electronics on the bike other than the tach which I removed to eliminate also.
I'm truly at a loss. Has anyone had bad luck with Electrex world ignition? I'm trying not to give up on it but I'm about to throw in the towel.
I don't pretend to know the answer but have you done a plug chop when it hits the limit? That would at least show what the fueling is doing.
I have, they are ever so slightly wet, but as far as color goes I'm in the ballpark. Gary sent those carbs with 210 main jets and I've had to go to 250 mains to get where I like the outcome. I've gone from 190-320 just playing around trying to make a difference.