2012 Gt Power Loss After First Service.

This one is a bit of a saga.
Just completed my 2nd sevice on my 2012 GT? After the first service, the vehicle seemed to show a loss of around 10% power. Mostly mid to top end of the rev range.
I have looked into every avenue that this problem may have been caused by. Fuel, Ford software updates, and everywhere in between. I even have accounted for the fact that I may have just become used to the power. I have ruled that one out due to several passenger comments on why it feels as if it is towing a heavy load. Seems that the only possible explanation is that during the service undertaken at my Ford dealership, the software in the ECU has been adjusted for economy and therefore lost some hp in the process. There were updates made during the service but of course the dealership says nothing has been amended. It is hard to pin down something as ambiguious the loss of power like this and harder to explain. Very subjective I know. Some other blogs have shown other GT owners with the same occurance. Some with solutions that slove the issue by pulling the throttle fuse for 20 mins and then re-installing. Not in my case. I have also tried a tuner to tweek the stock tune....and I am sorry to say that there was very little difference or none at all to the performance. Guessing that a tuner would adjust the existing perameters and I would see a substantial change. Is anyone had the same issue? Am I imagining this? I know I should put it on a dyno to see if it is close to any sort of published hp. I even connected an OBD monitor device and although I am sure the readings for HP, TRQ, and Power come out around 300- 320 RWHP. I have followed this over the lsat 6-7 months. I have come up with nothing. any ideas

They installed updates according to them. Not sure if that is considered a reflash of the PCM, I cannot say. It was from that point that I noticed the issue. My second service was recently completed and nothing was found to be wrong. I have looked into most simple solutions, such as disconnecting the battery and pulling the fuse to the throttle as I had read in a previous post that It solved a similar issue to mine. Nothing seems to cure it. There are no fault codes being thrown but I have noticed that O2 sensors are failing through an OBD test I ran. Not that I think that that has anything to do with it. It is just another thing to throw in to the mix of things. It really is hard to pin down. Just as a side note to the problem, I it feels to have more power at half throttle than at wide open throttle. In real time driving to compare, I was left in the dust by a V6. Just thought that that would be unlikely. Pretty frustraiting.