Lucy - The Red Super VR4 from Hell (Acceleration Problem/Boost Issue?)

First off, I'll link a video of the issue and tell me what you think it is. This or next weekend, I plan on changing the Spark Plugs, and doing a Coolant Flush and maybe a Boost Leak test.
It's done 258,000KM so I plan on doing a full service and giving her plenty of love in the hopes of solving this issue.
https://youtu.be/JnAVwieuGtk
So that cutting under boost is the issue, only happens above 3,500 RPM. If I don't put my foot down at all then it doesn't have a problem at all and drives fine. But once I put my foot down, give her the beans, it sputters, cuts for a second, accelerates slowly through the gears up to speed hiccupping as it goes. When it hiccups, it'll blow a bunch of black smoke out the back.
It's been to two different mechanics and they both couldn't figure it out/Grrr, so I figured get it WOFed and book it into the place where the transmission had been replaced (done at 245,000KM).
Recently had a new fuel pump installed because the mechanic wasn't getting anything from the return fuel line. Called him yesterday, and he said once he'd installed the new fuel pump it was getting fuel from the return line.
I have EvoScan so I can upload my EvoScan logs which sensors should I log as I do my runs?
What should I be checking in the engine bay? The mechanic checked all the turbo piping and said that was fine.
Any Mitsi/Turbo specialists down Dunedin sort of area?

I'm a new member of ClubVR4 and I found my chassis code in the forum post that mentions Super VR4s, which I am delighted about because I had my suspicions she was special.
Any help would be appreciated :d

That sounds a bit like the beginnings of the symptoms of MAF issues. Unplug the MAF and take it for a spin, obviously it won't perform normally and if it's an auto the changes will be weird but if the black smoke and hiccupping are gone that will confirm it. You'll get fault codes of course due to the baro, temp and airflow being missing.
If it is the MAF, read this thread I posted in here a while back on how to fix it:

https://www.clubvr4.com/forum/showth...ny-ideas/page3

Since you're in NZ (although you don't say where) if you do need a repair and can't get someone local to do it, I could do it for you provided you gave me return freight.

Replying to my own thread as an update.
Spark Plugs, Fuel Filter and Pump, Leads, now brand new coil packs!
The hiccuping turned out to be a boost leak, that's been sorted.
Still runs rich as hell when on boost, lots of black smoke. Tried multiple MAFs too, soon I'll have a whole 6A13TT with rod knock.
Figured I can use that engine for replacement parts and sensors.

So next question where should I be looking next?

What sensors should I be looking at replacing first?

I do have Evo Scan+Cable so if anyone is still willing to have a look at my Evo Scan Logs that'd be legendary.

Cars are pain.

They often run rich as standard, but boost leaks are the biggest headache. Ideally find someone who can do a proper boost leak check as often you are chasing your tail for hours when a boost leak check can find the issue in minutes.
I've made a DIY kit to run off my compressor but mechanics often have smoke sources etc to make it even easier.

It's had a couple boost leak tests done on it from a few different shops, I do plan on buying a lot of hose clamps and hopefully some new rubber lines and replace and colour code it from the workshop manual.