A well tuned 2/300 tdi have plenty of power if done correctly,
1st things I'd do, give the thing a good service, fuel filter and sedimenter at the back, fresh air filter, could have the biggest pump in the world if there blocked it won't get enough fuel,
Fit a boost gauge and check it making full boost, check the throttle cable is achieving full movement, water gate could be stuck open or not moving fully, split in a boost pipe? Delaminated boost pipe?
Once you are 100% everything is correct then maybe look at changing the fuel pump,