Mazda 3 on acceleration drops engine power

The first major symptom that appears when spark plug gaps get too big (from wear) is that you get a band of hesitation only at full throttle and somewhere well below peak torque. This is the band where the most voltage is required for a successful spark, because at this time mixture is most dense. Below this band the mixture is less dense because less mixture is drawn in with each stroke. Above this band the mixture is less dense because the spark occurs earlier in cycle (spark advance). The result is that this is the first rpm at which old plugs will misfire.

2100-2500rpm seems about right, but I don't know your car.

Check your spark plugs, or if you don't like (buying) wire gauges just replace your spark plugs. Cracked high tension leads also reveal themselves in this same rpm band.

The next step would be to look at sensors, but I'll wait for you to confirm that your plugs and leads are fine before going further.

At this engine speed the EGR valve is operated. A slow operation, caused by exhaust debris will cause this to happen. A second symptom would be intermittant rough idling.

Quick pointed question: Does this tend to happen when the fuel tank is nearly empty, or does it also happen when the fuel tank is full? It's possible that the fuel pickup tube is displaced or otherwise starving the vehicle of fuel under hard acceleration. That may result in normal acceleration until the fuel rail runs out of pressure, then the drop in speed would surge fuel forward to the fuel pickup tube again, which would permit you to resume accelerating.

This would ONLY apply if your symptoms did NOT appear with a full tank, though - with a full tank, the entire fuel pump is fully submerged in fuel.

It's a straw, but it's worth grasping at.