Many Trinitarians (such as myself) believe that Christ referred to the Father as his God, because (after the incarnation) Jesus was a human (and honored the Father as his God as all humans are to honor the Father as their God). As Paul Weathers stated: "Since Christ came as man, and since one of the proper duties of man is to worship, pray to, and adore [God], it was perfectly proper for Jesus to call the Father "my God" and to address him in prayer. Positionally speaking as a man, as a Jew, and as our high priest ("made like his brothers in every way," Heb. 2:17), Jesus could address the Father as "God." However, Jesus did not relate to the Father in this way until he "emptied himself" and became man, as it says in Phil. 2:6-8" Ron Rhodes quote of Paul G. Weathers in: Reasoning from the Scriptures with the Jehovah's Witnesses p. 152
Biblical support: The Bible does give an indication that Jesus addressing the Father as "my God" is specifically linked/due to his becoming a human at the incarnation:
Psalm 22
1: My God, my God, why hast thou forsaken me? why art thou so far from helping me, and from the words of my roaring?
2: O my God, I cry in the daytime, but thou hearest not; and in the night season, and am not silent.
3: But thou art holy, O thou that inhabitest the praises of Israel.
4: Our fathers trusted in thee: they trusted, and thou didst deliver them.
5: They cried unto thee, and were delivered: they trusted in thee, and were not confounded.
6: But I am a worm, and no man; a reproach of men, and despised of the people.
7: All they that see me laugh me to scorn: they shoot out the lip, they shake the head saying,
8: He trusted on the LORD that he would deliver him: let him deliver him, seeing he delighted in him.
9: But thou art he that took me out of the womb: thou didst make me hope when I was upon my mother's breasts.
10: I was cast upon thee from the womb: thou art my God from my mother's belly.
Isaiah 49
1: Listen, O isles, unto me; and hearken, ye people, from far; The LORD hath called me from the womb; from the bowels of my mother hath he made mention of my name. 2: And he hath made my mouth like a sharp sword; in the shadow of his hand hath he hid me, and made me a polished shaft; in his quiver hath he hid me;
3: And said unto me, Thou art my servant, O Israel, in whom I will be glorified.
4: Then I said, I have laboured in vain, I have spent my strength for nought, and in vain: yet surely my judgment is with the LORD, and my work with my God.
5: And now, saith the LORD that formed me from the womb to be his servant, to bring Jacob again to him, Though Israel be not gathered, yet shall I be glorious in the eyes of the LORD, and my God shall be my strength.
6: And he said, It is a light thing that thou shouldest be my servant to raise up the tribes of Jacob, and to restore the preserved of Israel: I will also give thee for a light to the Gentiles, that thou mayest be my salvation unto the end of the earth.
Micah 5
2: But thou, Bethlehem Ephratah, though thou be little among the thousands of Judah, yet out of thee shall he come forth unto me that is to be ruler in Israel; whose goings forth have been from of old, from everlasting.
3: Therefore will he give them up, until the time that she which travaileth hath brought forth: then the remnant of his brethren shall return unto the children of Israel.
4: And he shall stand and feed in the strength of the LORD, in the majesty of the name of the LORD his God; and they shall abide: for now shall he be great unto the ends of the earth.
The Watchtower however claims that Christ (even in his pre-earthly existence) had always honored the Father as "his God". If this is so, then why does it seem to be primarily in the future post-incarnation/human related prophetic scriptures that Christ is shown to honor the Father as his God ?