Help! Undiagnosed possible electro-mechanical problem

Hi Peugeot Universe

We would deeply appreciated any advice.
We have a very well loved Peugeot 307 2007 Diesel Automatik with a problem no-one can figure out.No code shows up.

Car starts fine, then as you start to drive suddenly there is no power( as in acceleration even if you floor it). Also happens after you slow down and then want to accelerate.
It's nerve wracking trying to cross big intersections because it may not have the power to respond fast enough.

What we have tried:
Overhaul of the vvt valve, changed air filter, changed the spark plugs, overhaul of the butterfly valve, injector cleaning product.

There was a slight improvement for 2 days after the butterfly valve but then it was back full force.

It's our family car and we really need it. But at this stage if anyone can't help us it may be cheaper to sell as is .

Really appreciate the advice/ input/ out of the box ideas