Slow acceleration, Black Smoke

Exhaust back pressure after the turbo.

Have you thought about getting a rear tech out there yet?

How many hours do you have on that motor?

I'm wondering if you don't need a valve adjustment.

Capt Fred did mention something close to that.
In the old days of Detroit fuel modulators, it would cause a similar problem just on fast acceleration.
As boost did come up, the smoke cleared.

You mentioned the injectors were checked, does that mean popped and matched?

I missed this post.
And sorry about the interruptions.

In watching the wastegate, see if it is operating at all.
It should start in the closed position. if it starts to move and your making smoke, try to push back on it a lil.
It is of course going to be hot.
Also, watch for it moving in rythem with that bouncing boost gauge.

Getting back to the fuel pump / governor over fueling.
Hard for me to explain but I'm still thinking not.
If we poor the fuel in, the expanding exhaust gasses should still come to the rescue and spin the turbo up and offer the air required. Big circle of parts working together.
Throttle delays and servos were designed to slow the fuel dump down a lil to keep the intermittent black smoke belch down. Even without these ad-ons, a not so fast throttle hand would do the same.
So, I'm still on the turbo / wastegate assembly followed by restricted exhaust.

Now, the techs, you did reserve one or all?

Ah, You had the turbo off?? Was the exhaust manifold and the riser can clean/clear? No carbon building up or clean, just covered in soot?
Soot in both directions? Both wheels dirty? Any stains or nics?
Shopping for a rebuilt turbo chunk yet? You may not need the whole thing, some tubos sell with just the center chunk.