Wouldnt hurt to get the fuel pressure tested.
Could be the regulator but the fuel pump could be dying.
Dirty air filter, & bad coils could all cause a lack of power.
If the EGR system isnt funtioning right that'll cause power loss.
The EGR tube get plugged after time and needs cleaned.
Vacum leaks, or low and uneven cylinder pressure could be contributing to the lagg also.
Over time hoses dry out and crack/leak. Cylinders leak
Hope that helps !