The ALDA is an anaeroid (sp?) compensator; effectively a fuel enrichment device while under boost, but also a fuel leaning device at high altitude.
The ALDA is the flat square device about 8cm on a side and 2cm thick sitting at an angle on top of the injection pump. It'll have a tube connecting it to the overboost protection valve on the firewall ahead of the brake master cylinder. The valve will have a tube connecting to the intake manifold above the injection pump. Make sure both lines are clear and that you can blow air from the intake manifold connector to the ALDA connector.
If the line is clear, TEMPORARILY connect the ALDA directly to the intake manifold and see if that yields improvement. The risk is that you're running without protection against the wastegate sticking closed. You won't have any problems if you don't keep the pedal to the floor for extended periods. You shouldn't have any problems if you do but you have less of a margin of safety.