Grannville,
I feel your pain, and have been there with a different vehicle. RR P38 (Petrol) Would start up normally, run for a few minutes & cut out. Sit for few minutes, start agian and run for hours. Shut down and let it get cold, sequence repeated.
Tried everything (including your extensive list) to no avail - even bought a new fuel pump (the expensive ones!!)
The most annoyting thing was no relevant faluts were being thrown - I was getting misfire warnings, plus other oddities.
It turned out to be the crankshaft position sensor. Unfortunatly they do not appear to fail in a black & white fashion, they seem to degrade over time and cause other faults.
This may not be same for the TD5, but for the cost of a sensor https://www.island-4x4.co.uk/crankshaft-crank-sensor-intermotor-nsc100790g-p-5846.html, it may rule out the problem.
Just a thought.
Best of Luck
Ken