Randel Helms from Gospel Fictions on Jesus' last words.

I typed this a couple of years ago after reading Randel Helms great missive. Gospel Fictions

In the second chapter Helms points out that in three of the four canonical Gospels that the alleged final dying words of Jesus are recorded differently, and Matthew spins the words for his own purposes. I will cite the text at length as Helms is a better writer than me.

"For example, according to Matthew and Mark, the dying words of Jesus were, "My God, my God, why hast thou forsaken me?" According to Luke, Jesus' dying words were, "Father, into your hands I commit my spirit." But according to John they were , "It is accomplished." To put it another way, we cannot know what the dying words of Jesus were, or even whether he uttered any; it is not that we have too little information, but that we have too much. Each narrative implicitly argues that the others are fictional. In this case at least, it is inappropriate to ask of the Gospels what "actually" happened; they may pretend to be telling us, but the effort remains a pretense, a fiction.
The matter becomes even more complex when we add to it the virtual certainty that Luke knew perfectly well what Mark had written as the dying words, and the likelihood that John also knew what Mark and perhaps Luke had wrote, but that both Luke and John chose to tell the story differently."

[The interesting thing here is that both the Lukian and Johnine writers were working from Mark and other source documents, but they choose to tell the story in very different ways for doctrinal and theological reasons related to the needs of their faith communities. This argues against historicity and reliability of the Gospels because if the evangelists were relating events involving the Son of God or God Incarnate they would have taken pains to ensure accuracy rather than incorporate many discrepancies and contradictions between the various Gospel accounts. Helms continues.]

"The Gospels are Hellenistic religious narratives in the tradition of th Greek Septuagint version of the Old Testament, which constituted the "Scriptures" to those Greek-speaking Christians who wrote the four canonical Gospels and who appealed to it, explicitly or implicitly, in nearly every paragraph the wrote.
A simple example is the case of the las words of Christ. Mark presents these words in self-consciously realistic fashion, shifting from his usual Greek into the Aramaic of Jesus, transliterated into Greek letters: "'Eloi eloi lama sabachthanei (My God, my God, why hast thou forsaken me? - Mark 15:34). Mark gives us no hint that Jesus is "quoting" Pslam 22:1; we are clearly to believe that we are hearing the grieving outcry of a dying man. But the author of Matthew, who used Mark as one of his major written sources is self-consciously "Literary" in both this and yet another way: though using Mark as his major source for the passion story, Matthew if fully aware that Mark's crucifixion narrative is based largely on the 22 nd Psalm, fully aware, that is, that Mark's Gospel is part of a literary tradition (this description would not be Matthew's vocabulary, but his method is nonetheless literary). Aware of the tradition, Matthew knew that no Aramaic speaker present at the Cross would mistake a cry to God (Eloi) for one to Elijah - the words are too dissimilar. So Matthew self-consciously evoked yet another literary tradition in the service both of verisimilitude and of greater faithfulness to the Scriptures: not the Aramaic of Psalm 22:1 but the Hebrew, which he too transliterated into Greek - "Eli Eli" (Matt. 27:46) - a cry which could more realistically be confused for "Eleian". Matthew self-consciously appeals both to literary tradition -a "purer" text of the Psalms-and to verisimilitude as he reshapes Mark, his literary source. ..... Matthew certainly knew that he was creating a linguistic fiction in his case (Jesus spoke Aramaic, not Hebrew.) though just as clearly he felt justified in doing so, given his conviction that since Psalm 22 had "predicted" events in the crucifixion, it could be appealed to even in the literary sense of one vocabulary rather that another, as a more "valid description of the Passion.
Luke is even more self-consciously literary and fictive than Matthew in his crucifixion scene. Though, as I have said, he knew perfectly well what Mark had written as the dying words of Jesus, he created new ones more suitable to his understanding of what the death of Jesus meant - and act with at least two critical implications: First, that he has thus implicitly declared Mark's account a fiction; second, that he self-consciously presents his own as a fictions. For like Matthew, Luke in 23:46 deliberately placed his own work in the literary tradition by quoting Psalm 30 (31):5 in the Septuagint as the dying speech of Jesus: "Into your hands I will commit my spirit" ("eis cheiras sou parathesomai to pneuma mou"), changing the verb from future to present (paratithemai) to suit the circumstances and leaving the rest of the quotation exact. This is self-conscious creation of literary fiction, creation of part of a narrative scene for religious and moral rather than historical purposes. Luke knew perfectly well, I would venture to assert, that he was creating an ideal model of Christian death, authorized both by doctrine and by literary precedent." - from "Gospel Fictions" p.15-17

Helms makes a good case throughout "Gospel Fictions", for there are many examples of this sort of purposeful editorial revisionism to assert midrashic theological-doctrinaire teachings. The last words of Jesus were and are of utmost importance to Christians as you yourself indicate by citing John 19:30. Yet each of the canonical Gospels tells it differently or spins it differently in the case of Matthew. This shows that the Gospel authors were self-consciously aware they were not dealing with history but rather with pious fiction. Taken together almost all content of the Gospels can be shown to be based on earlier Moses, Elijah, David stories or from bits of liturgical text form the Jewish apocrypha. I recommend Dr. Robert M. Price's book "The Incredible Shrinking Son of Man". Price does a masterful job of illustrating the midrashic nature of the Gospels.

In "The Case Against Christianity" Michael Martin evaluates Dr George A Wells' argument against a historical Jesus and concludes:

“Well's argument against the historicity of Jesus is sound, and recent criticisms against his argument can be met. So on the basis of Well's argument there is good reason to reject not only Orthodox Christianity but even those versions of Liberal Christianity that assume that although Jesus was not the Son of God he was an ethical teacher who lived in the first Century.” ~ p.67, ISBN 0-87722-767-5

My point in all of this is to note that the story of Jesus is fictional. Whatever Jesus really was, we'll never know. He is lost to history, and all that remains is a sad caricature clothed in layers of obfuscatory religions doctrines hidden behind the stained glass of orthodoxy.