[djcdmv]

Ever since I bought the car last fall, as soon as the car hits about 5500 rpm it looses power as if there was a rev limiter or something. I just recently had the car in for a oil pressure sender unit install at a local European Specialist. The tech was very impressed with how the car ran except for the loss of power issue. He said it pulls hard as it should up to 5500 rpm. He thought it could have been either an injector or possibly some sort of air line problem (my words, not his... can't remember what he said right now). Any ideas? Car only has 30,000 miles and he said he was amazed at what good shape the engine was in. I replaced plugs, wires, cap, rotor, and air filter last fall and it still occurs.
So:
1. What could cause the car to loose power while accelerating at 5500 rpm?
2. If there are several possible causes, how can you diagnose what it is?

Thanks in advance!