On a recent run down the coast I noticed that when I put load on the motor I lose all of my vacuum, so much so that my ventilation controls go to the default no-vacuum setting (Windscreen, heater on) Initially I suspected a leak, but this is not the case because at idle I have 20Hg rock solid. Open the throttle body and apply load and it will go to nothing. I suspected I was not getting enough fuel so I replaced the fuel filter wich was almost totally blocked. I then cleaned the injectors and fuel rail with metho, a syringe and 12Vdc. This gave a slight improvement. I have noticed that the timing does not advance very far when I give the throttle a blip in park, about 15-205 deg. My V8 ED advances significantly more than this. How far should it advance in normal mode in park? any ideas?

Doesnt really sound like a vac problem does it? I mean, the manifold will reach atmospheric pressure if the TB is wide open - but doubt the vent controls should be defaulting to windscreen.

Any EEC diagnostic information to be had?

The ECU gives 1 1 1, but I replaced it with a spare anyway. No change. I replaced the TFI module, No change. New leads, cap, button and plugs, No change. I blocked all vacuum connectors on the manifold, no change.
As a test I reversed the connections for fuel supply and return, the fuel pump sounded very laboured and stopped early, suggesting it is pumping at capacity. I would like to know if the timing is advancing enough.

Have you checked if the base timing is correct?

Has your vacum tank got a crack in it? that would cause vacum lose at full throttle or even the one way valve maybe faulty.

Base timing is correct and I have plugged all vacuum outlets on the manifold except brake booster and MAP sensor.