Very good points, especially since we can show that Jehovah's name (YHWH) was preserved over the thousand years of Old Testament transmission. So it is correct to ask why He did not preserve it in the NT, if it was ever there in the first place?
But even in the OT the correct pronunciation of YHWH is unknown. And maybe people didn't know how to pronounce it in Jesus' day either. That may be why Jesus never used it. Jesus used substitute words like Father, and the Power.
There are many times in the context of a verse or passage in the New World Translation where it is plain that Jesus is being spoken about, and the sudden appearance of "Jehovah" is distracting. For example, in Stephen's prayer at Acts 7:59, 60, Stephen begins by praying to the Lord Jesus, then suddenly the NWT changes over to "Jehovah." That makes no sense. The Greek text has "Lord" in both places, which does make sense.