A3 8l cutting out issue

[MarkD131282]

Looking for a bit of advice, my 8l has developed a problem with the revs dropping until it cuts out when pulling up at junctions.
On first start it’s fine and drives normally until it warms up then as soon as you put your foot down this issue with the revs starts.
It’s not stalling more like dying and sometimes you can see the revs drop below the tick over as if it’s going to die but just as it does it doesn’t if you get me.
It only starts to happen when you get a bit heavy with the accelerator.
It’s had a full service new coils plugs etc. 
I’ve recently changed the throttlebody as was told it could be that but it’s not cured it. 
Apart from changing the crank sensor I’m out of ideas now 😤