LOL it's not a diesel, it's a high revving race bred engine! Standard software cuts fuel injection (Hard cut) @ 7K RPM so that gives you some idea, these are electronically limited, there is no mechanical restriction in the dizzy!

The fuel pump voltage needs to be checked UNDER load, i.e when giving it a boot full in 3rd as this is when the pump pulls more power, as said also at the minimum (Check the fan wiring to make sure the fans actually work) but ideally rewire, these are two chronic weak points!

If it revs cleanly in neutral then it's possibly fuel related.

Martin