Hesitating and not revving out...

Any suggestions please.

D2 TD5, suddenly started spluttering or hesitating between 2500-3000 RPM (fine up to that) then wont rev out. Occasionally 'Water in Fuel' light comes on for odd second only.

Searched for solutions and so far...
1. Cleaned MAP sensor - it was a bit gunked
2. Tried running without/with MAF plugged - no different
3. Did find oil in Red ECU plug, so changed injector harness and cleaned though wiring to ECU over several days - no different
4. Unscrewed fuel filter drain and only BP's finest flowing, so assume usual faulty sensor?
5. Fuel pump seems to sound normal

NB - EGR is already removed.

Any suggestions on next move?

Thanks

Cheers

Dave

blocked cat?

Is there a quick way to check cat?

Oh and by the way, turbo actuator moves ok ish...