On the surface, you’d probably start looking at the car’s fuel system. A diesel, even a modern one, is controlled largely by how much fuel is being pumped into it and at what pressure. If the fuel pump is slack or the injectors, filters or lines are faulty or leaking, you might find that there’s simply not enough fuel to keep it revving on beyond that 2200rpm.

But you could also be looking at an exhaust problem, a partially blocked intake system, dirty air filter, or even a worn out turbocharger. A mechanic who is familiar with this make and model is going to have the best chance of diagnosing what’s wrong. Chances are yours is not the first vehicle to do this, and a specialist mechanic has possibly seen it all before.

The smart money here suggests that there’s something your car’s electrical system and body computer don’t like about replacement LED lights. That’s assuming you’ve installed them correctly, of course. The first thing you should do is replace the standard globes and see if that restores the lights’ operation. If it does, you can be reasonably sure there’s a problem with the way the car reacts to the LED replacements.

Not all cars appreciate the conversion to LEDs. These newer lights draw a lot less current than conventional globes and, while that sounds like a good thing, the lack of current-draw detected by the body computer can cause problems. Another common problem with LEDs is that the low current-draw makes the car’s computer think that there’s a blown globe at which point it can trigger a warning light on the dashboard.

Without being able to view it and hear it firsthand it's hard to suggest what might be wrong. It could be a bearing in the turbo, but that's only an educated guess. I would have a mechanic check it.