I might get another turbo, ill see how this one does at the track first. Just wanted to make sure something wasnt wrong with it before i went to the track and beat on it.
I mean there is a few things to check.....obviously boost leaks can cause slow spooling.
Check all the vband connections with the car running for leaks, you should be able to feel air around them if they are leaking.
You said on3? what kit... Front facing kit?
I just had mine tuned and it looked somewhat like that on the dyno, 4-5 psi by 4k, and only 9-10 psi by 4500 rpms and I had boost leaks out of all 3 v bands.
Now that I fixed the leaks, boost pretty much all hits at one time around 4k rpms.
Also, I know you said your running a manual controller, not sure how they work but with my eboost controller like I said earlier, you can set the wastegate to stay 100% closed untill say 19 psi and have it set to 20 psi and boost should come up really fast vs when I was running just springs, my boost looked like yours, almost like a centri blower.
Anyways, what size a/r are you running on that turbo?
You could try downsizing the a/r way down to try to spool it faster...maybe a .61 backside.
I know thats a big turbo but I would think it would fully spool at some point, that thing seems like it still hasnt stopped climbing at 6k?
How much boost was it set for?