As for the NT, we must first note the fact that there is no known evidence of the tetragrammaton in any surviving MS of the NT. If it were ever there, it has vanished without a trace. Secondly, as in the case of Philo, the presence of κυριος in the LXX is crucial to the interpretation of certain NT passages. Foremost among these is Ro. 10:9ff, where Paul states that salvation rests upon believing in the resurrection of Christ and confessing Jesus as Lord (Gk. . . εαν ομολογησης εν τω στοματι κυριοω Ιησουν). He then cites some OT texts which he believes support his assertion: Is. 28:16: “No one who believes in him will be ashamed” (Ro. 10:11); and Joel 3:5, “All who call upon the name of the Lord will be saved” (Ro. 10:13). The latter is a direct quotation from the LXX: πας . . . ος αν επικαλεσηται το ονομα κυριου σωθησεται. Even if one wishes to make God the Father and not Christ the antecedent of these verses (and this is by no means certain), the passage only makes sense based on LXX texts containing κυριος. How else does one account for the phrase “for the same is Lord of all” (ο γαρ αυτος κυριος παντων) in v. 12, just before the Joel quotation? The tetragrammaton would not make grammatical sense here. It is far more likely that Paul is making a Christological statement through a deliberate juxtaposition of κυριον Ιησουν and LXX references concerning the saving power of God, ο κυριος. (Sean M. McDonough, YHWH at Patmos: Rev. 1:4 in its Hellenistic and Early Jewish Setting [Wipf and Stock: 2011], 61).
This should be something that Latter-day Saints should raise with the Jehovah’s Witnesses we encounter who claim that the New World Translation is correct in “restoring” the divine name, “Jehovah” into the New Testament texts instead of “Lord” (κυριος). There is absolutely no textual warrant for this, and much of the New Testament and its theology is rendered nonsensical, as seen above, if one assumes the “original” NT manuscripts contained the tetragrammaton.