2.5TD 1996 Powerloss after 20km

[nofftello]

Hello everyone.
Maybe this was asked before and you can direct me where to find the threat.

We bought a Transit hitop van 2.5TD automatic, 1996 with 229'tkm. We are in Queensland, Australia.
It seemed the perfect campervan basis, however, not long after the purchase, we got a problem with the power output.
It drives perfectly for 20km, but then suddenly, it doesn't react to the gas pedal anymore. You can use push it through and nothing. Max speed is 60-70km/h.
We had so-called specialists looking at it. It must be now up to seven of them.
None could fix it or find the issue. Most didn't charge us and were happy for us to pick it up again.
Ford refused looking at it, too old!
However, we ruled out a few things in the meantime.
-fuel pump, fuel filter, injector pump, EGR valve (blanked), turbocharger, no rubbish in the fuel tank, all cables and connections seem fine. no crack in the manifold...
We are so frustrated that we are now planning to put it to the auction just to get rid of this headache.
What a nightmare..
It's so sad, as it has been very well maintained by the past owner until 2018, but then it must have stood around for some time.
Still, it starts great, and drives so great for the first km's.
Funny enough, when we took it onto the motorway, it even lasted for 50km without issues. Running easy 110 but then powerloss and only 60-70 max.
It seems start and stop reduce the distance it lasts.
If anyone has any idea, much appreciated.
Thank you.

[MinorMatt]

Sounds temperature releated.

Have you managed to find anyone who can read the fault codes?

This is total (educated) guesswork but I would try (in this order)

Carefully inspect both sides of the connector to the back of the injection pump for any damage or corrosion
New coolant temperature sensor (the ECU - not gauge one) - it sticks out of the left hand side of the thermostat housing - not the one pointing towards the rocker cover
New/Replacement injection pump cam position sensor (its the one under a plastic cover you can see on the side of the injection pump)
New Air intake temperature sensor - on a 1996 this should be on the air filter box.