Q: Power loss 3000 to 4000 revs - Mazda3 2.0L sport 2005

Something like this sometimes stems from a sensor(s) falling out during the indicated range, that is the signal falling out. Such could involve the throttle position sensor, mass airflow sensor, or perhaps sensors involved in advancing ignition timing. EGR system malfunctions are also a possibility. Typically a real time automotive scan tool, which is viewed by the mechanic during the "window" of misoperation, would yield answers as to what is going on. Key engine operating parameters are viewable on such a tool. What I would suggest is you request an engine loss of power diagnostic. If you request that diagnostic, the certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.