[Aiden]

Thanks for your help,
The engine had head gasket problems since I bought it last year but the performance seems fairly similar before and after the rebuild. The exhaust system wasn't changed, just thought I'd mention that it looks very rusty on the outside and so may be clogged?

The loss of power under loads has only happened 2 or 3 times and seems to be something like a wastegate opening or perhaps the egr because it only lasts for a few seconds and is at full boost (+3k rpm).

I have the egr switched off electronically using the idle cut-off switch wired into a new switch in the cabin (for emissions tests/city driving), but may replace the blanking plate since I doubt it has much effect.
I recently cleaned out the intake manifold, and have only ran the egr for a few hours since, so that should be fine.

I went with an experienced mechanic who worked on the engines a decade or so ago, but I think much of the work was done by a colleague without any experience with the platform. I also gave him the green book for the N/A D24 for reference so he may have timed it incorrectly if there are differences with the turbo engines.

With the engine running as well as it is (+40 mpg on a run) I would guess that it's either a tired turbo or something that would only limit to end performance (3 notch gasket?).
Hope this helps.