I guess you'll have to define "boasting", then. In one sense you are absolutely correct - Jesus came not to do His own will, not to speak His own words - but to do that which He saw His Father do and speak that which His Father gave Him to say. He came to bear witness to the truth - not to elevate Himself. But that was because He came for a specific reason. In that sense, He deflected all attempts to be publicly exalted during His earthly ministry. Satan tempted Him in that way, Peter resisted Him in that way and crowds wanted to make Him an earthly king. Yes. He rejected all this. But on the other hand, the claims He made for Himself were outrageous (if they hadn't been true, that is). For anyone else to claim what He did would have been well beyond boasting - it would have been outright blasphemy.
But again, whether Jesus boasted or not is in the broader context of why He came. As has been pointed out, the way He came the first time will not be in the same manner - nor for the same purpose - that he returns bodily to earth.
I guess what I'm saying is - why is the boasting issue important? I'm not saying it isn't, but how would it be wrong for the Creator of all things to boast? It's an entirely different issue with Him than it is with us?
For Jacob my servant's sake, and Israel mine elect, I have even called thee by thy name: I have surnamed thee, though thou hast not known me.
I am the Lord, and there is none else, there is no God beside me: I girded thee, though thou hast not known me:
That they may know from the rising of the sun, and from the west, that there is none beside me. I am the Lord, and there is none else.
Isaiah 45:4-6
For thus saith the Lord that created the heavens; God himself that formed the earth and made it; he hath established it, he created it not in vain, he formed it to be inhabited: I am the Lord; and there is none else.
Isaiah 45:18
Tell ye, and bring them near; yea, let them take counsel together: who hath declared this from ancient time? who hath told it from that time? have not I the Lord? and there is no God else beside me; a just God and a Saviour; there is none beside me.
Look unto me, and be ye saved, all the ends of the earth: for I am God, and there is none else.
Isaiah 45:21-22
Remember the former things of old: for I am God, and there is none else; I am God, and there is none like me,
Declaring the end from the beginning, and from ancient times the things that are not yet done, saying, My counsel shall stand, and I will do all my pleasure:
Calling a ravenous bird from the east, the man that executeth my counsel from a far country: yea, I have spoken it, I will also bring it to pass; I have purposed it, I will also do it.
Isaiah 46:9-11
Could Jesus not have justly said all these things? Would that have been boasting? Was it boasting when said through Isaiah?
Again...my question is what do you mean by boasting and what is the import of that? Your OP sentence runs on a little and is a bit hard to understand (clearly, that is). Explain what you mean by boasting and why you believe Jesus never boasted.