Flat spot

Hi all
Got issue with my 300tdi, she will rev just fine when not driving, but as soon as u drive her, she will get to about 3k revs and then that's it just hits a flat spot and won't go any more with foot flat to the floor.

Seems to boost up ok in first and 2nd but after that she is flat.

Tried new lift pump, and filter still the same.

Checked diaphragm on pump and all looks fine, checked for air leaks and pipes collapsing under load but again can't find any issues there

I'm thinking it may be pump itself or injectors but not sure. Anyone had this before or know anything else I could try??

Cheers

have you tried the usual suspects of the tank connectors / sedimenter if its in a disco, or just checking for damaged pipework - certainly sounds like fuel starvation.

Worth fitting a boost gauge, even if only temporarily, to check that you are getting the boost all the time, and the pipes aren't leaking.

Yea checked all the above