Matthew 27 and Mark 15 both say Jesus said "My God, my God, why have you forsaken me?", was offered vinegar, cried out again and died.
Luke 23 says that Jesus was offered vinegar more than three hours before dying, and said several things afterwards. It also says that his last words were "Father, into your hands I commit my spirit."
John says that Jesus said he was thirsty and was given the vinegar. From there, he said "It is finished" and died.
These words are from NIV, which actually includes the Aramaic for Matthew and Mark, though it spells them differently. (Hrm. So, those are also inconsistent. Hrm.)
So, we have two disparate timelines, and three distinct versions of what Jesus's last words were. Which of these is correct?
If we go with the first account, in Matthew and Mark, then both Luke and John are incorrect. If we go with either Luke or John, then three of the Gospels are incorrect.
We have a situation here where clearly there is error in the Bible. It cannot all be literal truth if there are three statements here that contradict each other.
If the Bible is not all literal truth, how can we (as mere, flawed humans) determine which parts are literal truth and which are not? Can we honestly have any faith in the absolute literal truthfulness of a work which is clearly not absolutely literally true? What percentage of the book, then, should we believe to be correct, as it clearly is not 100% so?
I cannot put my faith in something as literal truth when I know it is flawed. I cannot put my faith in something as the word of God when it clearly has had thousands of years of men's hands in it.
Consider, as recently as 1960, in a tremendously well-documented society, a man was born in Hawaii, and yet 50 years later we have people who believe AS ABSOLUTE TRUTH that he was not, and writing about it, and broadcasting their misunderstandings. In 1,000 years, if those were the writings found by future archaeologists, they would come to the conclusion that the man was not born in Hawaii, despite the well-documented reality of the situation.
From a largely pre-literate society, where some people had something to gain from making the fish a little bigger in their fish stories, I have negligible faith in the surviving writings as literal truth. Especially when they contradict each other.