2006 Ford Mustang Transmission Problem

Hi I have this mustang back in my garage with this strange trasnmission problem. So the problem is in the gear changes the transmission goes neutral as if it looses oil pressure and after that it goes to the next gear. Mostly from gear 1 to gear 2 but after driving the vehicle for few minutes the problem changes to gear 3, 4, 5 doing the same thing. I replaced every single mechanical part in the transmission and there is no codes on the scanner. Can it be from the transmission case or what else can the problem be from?