GPz750 won't rev over 8,000 rpm?

Since you have reinstalled the factory air filter box, it might be wise to restore the factory jetting as a starting point.
Based on some internet searching, that would be-
Needle: 4BC6
Main: 110 (112.5 if originally sold in Canada)
Pilot: 37.5

When the PO went to pods and aftermarket exhaust, he or she may also have installed an aftermarket jet kit like those sold by Dynojet. Their needles typically have a very different taper profile from the stock needles and their jet numbering system is quite different from the stock parts. I understand that trying to mix the two will lead to much frustration.

What does it do when you're at the rev limit and you engage the choke?

It dies

Okay. That is a strong clue I think.

My understanding is that this model did have a rev limiter built into the igniter. I don’t recall where I read that and I haven’t tested any of mine to see what the limit is. If that’s the case, I’m thinking perhaps as the igniter aged a component or two (electrolytic capacitors are the usual suspect) changed value and the cutoff threshold drifted downwards. 

Looks like the job is done, success!
My thinking was wrong, because I thought the Uni high flow filter and the 4>1 exhaust would need larger main jets. So I started with 115 and moved up trying 120 and 125 jets.
After moving back down to 115 jets it improved, so I dropped down to 110 jets, the original OEM size.
The 110 main jets did the trick, it's done 10,000 RPM in 2nd, 3rd and 4th gear topping off off at 110 MPH and eased back down to 70.
This bike I'm keeping stock, no intention to upgrade anything. I've had to service engine, carbs, brakes, steering bearings, fork oil and new tires.
Only 12,271 miles on it as of today.
Ω

Great to hear that ya rebel!! Did You have Annie Oakley or Jerry Reed running interference Bear control for you? This is what i've been advocating for years regardless of carb type, bigger isn't always better. But i think you'd already known that from the beginning. Hopefully You won't get one of those Flock Camera instantaneous generated Speeding Tickets in the mail ha. Have a Fun Gratifying Day of completion!