You might try this : Run up the motor. Open the rear hatch and with a hose or stethoscope, listen around the coils as you pick up the rpm's.
Listen for a ticking...not the EVAP Valve. It is not uncommon for the coils to break down.( Most replacement coils read very low ohms, below the Subaru specs if you check the new ones..)
As the engine picks up under load, the ECU leans out the fueling to the point it becomes hard to fire off. If the coils are not up to snuff, they fail to spark the plug/s under these conditions.
Another way of checking coils is to spray them with water from a spay bottle....best done in the dark as then you'll see the spark/s.
Another check you can make is to disconnect the O2. This will cause the fueling to richen up slightly. test drive to check fro any change. reconnect O2 after test and clear code/s if set.
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Remaining problem is low speed hesitation. Engine sorta stumbles upon part throttle low speed acceleration, especially up-shifting. May be worse when cold. Surges if allowed to fall to low speed in gear with no throttle (say rounding a neighborhood corner in third gear). Runs fine on the freeway. Makes smooth driving kinda tough.
