KZ440 Keihin Carb Issue

I'm all complete the restoration of my KZ440C. It looks great, runs great, has lots of power but just a couple issues.
When I go to shift gears, the RPM hangs up and stays reving for a couple seconds in between shifts. If I wait long enough or decelerate with the clutch engaged, the rev's come down ok. So the way it is now, the rev's stay up until I shift and release the clutch and then they are forced to come down. This is not the right.
I have very little experience with these carburators. (actually none)
The throttle slides snap back into place fast so I doubt it's that.
I am wondering if the diaphrams are too old and not responding quick enough? They seemed soft and supple when I rebuilt the carbs.
Any suggestions?

You have air leaks, most likely from the carb boots that attach to the head.  The entire carb system needs to be airtight or the idle will hang as you mention.

Don’t forget to buy OEM Kawasaki carb holders if you’re going to replace them 

They looked in good shape when I reassembled the engine. I'll try the propane trick first to see if that shows anything. (open up the valve on a handheld propane torch and slowly blow propane around the carbs and holders to see if the engine RPM changes)
If not then I'll still take it apart and reassess them.
Thanks

Are they still available in OEM? I'll have to check on Monday.

OEM will run me about $140 with new clamps.
These on eBay are $30 free shipping form Ontario (where I live) Might be worth the gamble???
Ebay Carburator Boots

No, I’m on this road now. Don’t do it. The cheap ones suck and you will have a worse air leak than you started with. Just pony up the $ once and fix it right. I did what you want to, paid $20 for some Amazon ones, now I’m waiting on my package of Kawasaki OEM ones to arrive to fix the problem like I should have done in the first place. Set me back $130 but it will fix it right. Buy once cry once. 

A couple of things to try before buying the boots:  Perform a vacuum sync, if you haven't already.  And richen the mixture via the pilot screw.  Try 3 or 3.5 turns open and see if that helps.

 I will definitely look into the vacuum sync.
As for the air mixture screws.? On this bike,  every single nut and bolt was removed, cleaned, polished and or repainted if it needed it on this restoration.  The only 2 things I couldn't do, were the two idle mixture air screws as they were seized and the heads were stripped. A previous owner must must tried to adjust them.  I was able to run carb cleaner through all the ports on the carb so I was just hoping the screws were seized in the factory position. 
i had posted online to see how to remove them but never received an answer. I used a dremel to make a new slot, tried a jewelers torch to heat the area, tried tapping to loosen threads.....nothing. Ended up just hoping.

When I rev it up in the garage it seems pretty normal. But when driving it seems to hang up more than this on the video below.

KZ440 RPM