This is how it has always been explained to me:
When Jesus called the Father "my God" he was recognizing his humanity and acknowledging Him as "my God." Prior to Him coming to earth in human form, He had only a divine nature. In this divine nature, He could never refer to the Father as "my God" because Jesus was fully equal to the Father in every way. It was only after the incarnation and taking on human form, that it was proper for Him to refer to the Father as "my God."
Also, Jesus always refers to "My Father" or "Your Father" but never "our Father." He was distinguishing the two because He is a son of God by NATURE and we are sons of God by ADOPTION.
Can you please explain what you mean about the JW's not believing in the physical resurrection of Christ? How do they explain the passages where Christ appears and walks with the disciples, and where Thomas places his hand in the holes in Christ's hand and side?