If your chain stretched and they reset the injection timing... but did not put an offset key into the cam sprocket... ( if it needed it ).. then you might check your chain stretch and see if you are over the amount suggested as acceptable...
According to the factory shop manual... when there is any performance complaint you MUST use the movement of the number one intake valve in the number one cylinder as your reference point...
Lots of good threads about how to do this correctly...
In other words... they might have only corrected the ip timing ... because that is relatively easy and quick... and not known about the need to keep the sprocket's relative position corrected also...which of course is your valve timing...