Did you check to see if maybe you just blew off an intercooler hose? Because I just discovered about an hour ago that that's what was wrong with my blacktop SR, and I have almost the same situation.
Been driving the car with stock exhaust for 2 weeks. Put on a 3" exhaust, test pipe, and aftermarket elbow the other day. Car drives fine for a while, until I hit boost hard and get up to 60, at which point it spews black smoke out the exhaust and sputters and coughs and won't stay running unless I nurse the gas pedal. Eventually discover popped off intercooler hose, re-attach, and all is peachy.
I'm guessing that my car naturally boosted harder because it was no longer restricted by the stock exhaust, and that increased boost was enough to blow the hose off (which I found out wasn't even tightened by the former owner
). Since you upgraded your turbo, I can only guess that the same thing happened to you
