You have to remember that the base tune of the 2.7 will be conservative and as the computer monitors the engine, it likely starts advancing the timing, trimming fuel, and playing with the camshaft timing within the parameters that Ford engineers allow. What this means is that the motor, following a ECU reset will require time to adjust all the parameters to get the motor to work at its peak efficiency and power. I would fully expect this to be the case with any modern engine ECU. For instance, the motor makes 400 ft/lbs on 87 octane, but feed it higher octane (91/93) and the ECU will adjust fuel trims, timing, and cams to take advantage of the additional octane. Put bad quality gas in it and the knock sensors will put an end to that quickly, lowering the power significantly. Reset the ECU and it will start from the most conservative tuning parameters and advance forward until the engine sensors provide data or engineering limits are reached to reign in the party. That's why early on, it may not be running at its highest possible output.
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