The Septuagint sleight is tricky and neato, but that doesn't really get us out of our problem seeing as how Jesus never referred to himself as IHVH, or the capitalized LORD. And too, IHVH in Zech. 14 is clearly speaking of THE IHVH of Hosts. I'm not attempting to diminish from Christ who has been exalted to the Father and has all power in Heaven and Earth, I'm simply saying that I'm not seeing IHVHs Messiah in Zech. 14. I'm seeing IHVH Sabaoth.
Zechariah could have easily used language such as 'In that the day the LORD's Messiah shall do such and such', or 'The feet of the LORD's Messiah shall stand on the Mount of Olives'. There's just one problem: that isn't what Zechariah wrote.
First, let me make the claim that the Septuagint Greek is probably more reliable than the Masoretic text. If it is not a close call, I will choose the LXX over the MAS. As for Zech 14:3, the MAS doesn't follow the storyline that began in 13:7, while the LXX does. Therefore, I don't think you can go wrong with the LXX in Zechariah 14.
As for the Trinity, Jesus claimed He was the Father, twice:
"I and my Father are one." -- John 10:30
"Jesus saith unto him, Have I been so long time with you, and yet hast thou not known me, Philip? he that hath seen me hath seen the Father; and how sayest thou then, Show us the Father?" -- John 14:9
Either we believe Christ, or we dont. I believe Him.
John said the world was made by him (which would be a pretty neat trick for someone who is not God):
"All things were made by him; and without him was not any thing made that was made. . . He was in the world, and the world was made by him, and the world knew him not." -- John 1:3, 10
Paul implied that Jesus considered himself equal to God:
"Who, being in the form of God, thought it not robbery to be equal with God:" -- Phi 2:6
And Paul either implied God and Christ would come at the same time, or they are one and the same:
"Looking for that blessed hope, and the glorious appearing of the great God and our Saviour Jesus Christ;" -- Tit 2:13
Even in the Old Testament Jesus is referred to as God the Father.:
"For unto us a child is born [Jesus,] unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace." -- Isa 9:6
I hope you can see why I have no problem believing that Christ is God the Father. But if that is not convincing enough, let's hear it from God himself:
"Look unto me, and be ye saved, all the ends of the earth: for I am God, and there is none else. I have sworn by myself, the word is gone out of my mouth in righteousness, and shall not return, That unto me every knee shall bow, every tongue shall swear." -- Isa 45:22-23
"But why dost thou judge thy brother? or why dost thou set at nought thy brother? for we shall all stand before the judgment seat of Christ. For it is written, As I live, saith the Lord, every knee shall bow to me, and every tongue shall confess to God. So then every one of us shall give account of himself to God." -- Rom 14:10-12
Are we bowing to God, or to Christ?
I almost forgot this one. Sorry for the late edit:
"Who shall not fear thee, O Lord, and glorify thy name? for thou only art holy: for all nations shall come and worship before thee; for thy judgments are made manifest." -- Rev 15:4 KJV
That sorta narrows down the list of Holy people, as well as the number of deities, which should not be too much of a surprise:
"And Jesus answered him, The first of all the commandments is, Hear, O Israel; The Lord our God is one Lord:" -- Mark 12:29 KJV
"And the Lord shall be king over all the earth: in that day shall there be one Lord, and his name one." -- Zec 14:9 KJV