Well make sure the tank vent blocked is not an issue. Try running with the fuel cap loose. Or when power drops hop out and undo the fuel cap for a second. Big whosh and engine is then normal for awhile is equal to blocked/obstructed tank vent.

At 150k I doubt the injection pump is actually worn out unless it has had a pretty good water diet. Also make sure your relief valve on the pump is overflowing when this occurs. You may have sagging pressure with the fuel supply.

First do the test with the car cold and then again when the difficulty is there. With no relief valve overflow at the pump with the engine cold the fuel is not acting to cool the injection pump where it is important to do it. Also indicates something is wrong.

Or drive the car until the problem occurs and clamp the return line from the injection pump off. Power increase a lot or not? The results of that one test alone would indicate something. A badly obstructed vent hose from the valve cover might cause some difficulty with a hotter engine as well. Easy to check.

The electric boost pump you installed. Location and psi? This is or is not a wvo car?