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The first thing I would recommend is checking for fault codes. There may be a code set that can be used for a starting point in diagnosis.
There are many things that could be causing your loss of power.
Low fuel pressure will cause a loss of power on acceleration. Fuel pressure can be monitored with a gauge while it's acting up, if pressure drops off then you know you have a pump or regulator problem. The pressure spec is 48-55 PSI.
You could have a restricted catalytic converter, which will block exhaust flow out of the engine and rob power.
An oxygen sensor wouldn't be that likely to cause this but is definitely possible. The throttle position sensor, or MAP sensor could also cause a lack of power.
Variable valve timing issues, lost or erratic cam or crank sensor signals or cam timing can impose a low rev limiter or reduced power mode also.