My guess is the motor is fine. As CC said, it doesn't care what the pump is doing and it is usually thermally protected. If overloaded as from sustained high pressure, it would overheat and protect itself. As you said it sounds fine, no new noises, just the slight pressure drop. As CC said that could be deformed pump parts but at this point I'd just live with it unless you feel in an inquisitive mood and feel like ripping it apart to find out for sure. Maybe some life was used up and it could die in a week (unlikely) or years from now.
Al