high rpm + high boost = stumble

[Bernard Littau]

My 5ktq is experiencing a stumble or mis-fire at high boost and high rpms.
I would dearly love some advice as to how to best diagnose this problem, and
ideas as to what the problem might be.

High boost is 1.6 - 1.7 bar, I am running a 1.7 bar spring and no WGFV input
to the WG.  ECU is good to 2.2 bar.

At any rpm, under low load and low boost, the car seems fine.
At low rpm and high boost, that is 5th at 3000 rpm, 1.7 bar, car seems to
run fine.
At high rpm, high boost, that is 3rd, 4000-6500 rpm, 1.6-1.7 bar, the car
stumbles or mis-fires.  It's not a subtile stumble, either.

The car is an '88 5ktq.  It has a new turbo, and the intercooler has been
converted to single pass.  I have great confidence that there are no leaks
in the air induction path from air cleaner to TB.  I do believe I have a
small leak somewhere in the manifold (a hose) as my idle is now at 1000 or
so.

What the problem is likely not:
I just replaced the wires, plugs and cap with new.  Plugs are: W7DTC 0.8mm
Rotor and distributor are 3 months old.
BOV has been removed and there are currently 2 pieces of 1" dowel in place
of the BOV.

I just replaced the turbo( IA RS2), timing belt and WP.  I also put in new
injectors -- everything beyond the flare-nut fitting is new.

The car ran fine at >1.7 bar at any rpm before I did the turbo and belt and
injectors.

Any thoughts are welcome and appreciated.

Best,

Bernard Littau
Woodinville, WA
'88 5ktq