"Neoliberal historical Jesus scholars think they tell the truth because the Gospels are not what happened.
Ecclesial Jesus scholars, like [Martin] Kähler, it is well known, and his more recent incarnation in Luke Timothy Johnson, tell the truth, whether it happened or not. The truth, they say, transcends what happened for it is the significance of what happened that is the truth.
Modernistic historical Jesus historians, some of whom would be Evangelicals, often believe that the Gospels tell the truth about what happened, and what happened is the truth, which, as is also well known, puts a big twist in their knickers if they discover that what they thought was the truth--that is, what happened--was not what happened, for it is therefore not the truth."
(Scot McKnight, "Telling the Truth of History: A Response to James D. G. Dunn's Jesus Remembered," in Memories of Jesus: A Critical Appraisal of James D. G. Dunn's Jesus Remembered, ed., Robert B. Stewart and Gary R. Habermas [USA: B&H Academic, 2010], 51. Emphasis original; paragraphs added.)
I see these three examples are basically different in degree of confidence over the text's description of historical realities. My position is unashamedly the third one when it comes to the four gospels. Why? I'll need to write a trilogy myself to attempt an answer!
But broadly and briefly, I think we cannot settle the problem of how much degree of confidence should we confer onto the gospels by merely analysing the texts. We need to widen our textual analysis to include literatures contemporary with the gospels, like what Richard Burridge did. There is also a need to analyse the immediate reaction towards these literatures, like what Richard Bauckham did with Papias' relation to the transmitted tradition about Jesus.
There is no short of the need to understand the various facets of 'memory' in the ancient world like oral history, eyewitness testimony, cultural memory, etc. Then the debate over metaphysic (supernaturalism or naturalism?) is inevitable as the gospels contain accounts that were surprising even to their first readers. Following from that, the studies on the philosophy of science has to follow as it will always came up whether if the assumptions underlying the scientific enterprise contradict historical claims, even claims that are apparently scientifically incredible. Then, the discussion over contemporary epistemology is warranted when we have to justify various level of belief on these ancient literatures. These are just the few pertinent issues off my head.
Even if the trilogy made it to the printers, a few months later, assuming that the project is widely be accepted and has almost no dissenters (which is impossible), the appearance of some new discoveries in any one of the above mentioned areas will effectively place the project for reconsideration.