The trinity is clearly present throughout the Old and New Testament.
Citation needed. Nowhere will you find the word "trinity", nowhere will you find "The Father, the Son, and the Holy Spirit" spelled out directly. The Trinity is inferred, a theological construct. In this particular case, I have no objection to it, but we shouldn't pretend it is literal scripture - it is derived, indirect theology.
You are correct that Christians today do use terms which are not found in scripture - word for word. We use terms like rapture to describe the events as written in 1 Thess. 4, 2 Thess. 2, and Revelation 4:1 (hereafter being after the church age of Rev 1-3). It is easier to just use one word that is understood among believers than to read out 1 Th. 4 every time you want to talk about the event.
The idea that all believers will vanish and disappear into the sky is said nowhere directly in scripture. The Left Behind series has about as much to do with the Bible as Taco Bell has to do with Mexican cuisine. The entirety of rapture theology was conceived in ~1830 - so it didn't exist for most of the church's history.
These are literal Bible truths.
They aren't. They are indirect interpretations made by humans, but you've read the bible in that light for so long that you don't see any other possibilities there when you read it.
My point is, biblical literalists often aren't really taking the literal meaning of scripture - they are taking one specific interpretation of scripture, a certainly flawed theological construct (being developed by humans, and diverging significantly from past doctrine) and claiming that it is the only possible interpretation.
You decry the schisms within the church, but in my mind the phony appeals to Biblical literalism, and every denomination's tendency to mistake theology for scripture, is exactly the problem. We must admit to one another that even if the Bible is divinely inspired and completely flawless, our individual readings of it will always be slightly different and mistaken, and hence we shouldn't get too caught up in any specific brand of systematic theology because we are all certainly mistaken in one detail or another.
The point being: we can say, with no doubt whatsoever, that Love is the priority of Christ. The bible communicates this both taken as a whole and taken as specific verses. Holding this belief also will tend to make us act more like Christ. The rapture, on the other hand, is clear only if you interpret many different verses in very specific ways, and it isn't clear how it fits into the overriding message of Love. What's more, it causes its adherents to behave in very un-Christlike ways... after all, if this world is going away, why care for it? If people's souls are all that matter, we should just evangelize to them and ignore their earthly troubles, right? This is an attitude not at all in keeping with Christ's actions, and this theology produces very "Bad fruit" in believers, so why defend it?
Let's be true literalists, and humble ones, and focus first and foremost on those things that are unilaterally clear from the text, and be willing to compromise on anything that is an indirect derivation of scripture. This attitude will tend to unite us by promoting the things that all Christians already affirm, and it also has the fortunate tendency to move contentious issues into the sidelines, where they belong.