2007 1.9tdi BXE surging and hesitatip

Hi, hoping someone can assist me.

For the last few months my car has developed a surge of power at 1800 revs, most noticeable in first and second but also cruising in 5th as long as the revs are between 1800 to 2000rpm.

The surge is powerful enough to thrust the car forward and continues to do so even when off the throttle pedal but luckily only lasts a second or two.

Also when driving at around 70 the engine will suddenly hesitate like a sudden loss of power but can be powered through on the throttle.

No fault codes on VCDS, have replaced MAF and Turbo, fuel filter, and had injectors and EGR cleaned.

Skoda garage want to replace the tandem pump but only as a guess and can't explain why this may be a cause?

I would greatly appreciate any assistance

Many thanks