Exhaust smoke is the best tool for diagnosis.
When it loses power is there any smoke? If not, disregard the above post.
To me you are dealing with lack of fuel supply to the injection pump.
So you have removed the gauze filter in the pump ay?
That may now be the issue or the new(ish) filter is partially blocked. If any crap (even microscopic) gets into the pump it can cause this too.
Forget what you have done in the past and start again.
Think I'm half way to a box of beers
Cheers,
