One other question occurring to me to add to ngoma's list above -- does your engine have EGR?
The EGR system (when present) on these D24T/IC is a very early design that uses stone-age controls relying on a half-dozen components that all can fail and have zero ability to self-diagnose. These include some electrical and vacuum switches around the throttle lever, a few solenoids and control units, a thermal vacuum switch etc. All very unsophisticated and vulnerable to failure in old age, and unable to alert you to any issues.
If your engine has this EGR system, then it might benefit your diagnostic process to temporarily or permanently disable it and see if that changes or eliminates the intermittent power loss you notice. If one of those switches or solenoids does the wrong thing at the wrong time and the EGR valve gets commanded open while you are running at full load, it could cause what you have been feeling. In fact it is hard to imagine much else that could cause a momentary power loss like this on an otherwise simple mechanically controlled engine.
The EGR equipped engines ALSO have the tendency to constrict the intake manifold passages since the carbon soot from the EGR can mix with oil vapors from the crankcase vent return, forming a cokelike hard substance that adheres to the walls of the intake runners like heart disease. Not commonly known to be a performance issue on D24T/IC engines, more just a mess, but then again, most of us have not been able to test the top end performance of our engines like you have.
If this were present and restricting airflow, you would notice it most in a situation of high speed operation. Probably wouldn't notice it at all in short bursts of low speed acceleration.
Search images of "TDI clogged intake manifold" for an illustration of the worst-case for how this can look, although again D24 type engine doesn't do it as badly as those do.
If you don't have EGR then of course all of this is irrelevant to your situation.
