Actually, some conclude that the scriptural evidence goes back further than the New Testament. There is a 3.5 hour lecture on Youtube from Michael Heiser demonstrating the doctrine of the Trinity using only Old Testament sources. He concedes that a duality is easier to demonstrate, but concludes that the Trinity is there if you want to “see” it.
Heiser is a Hebrew instructor currently working for Logos Bible Software who is also an expert on ancient religions.
Thanks...I'll check it out. I agree that duality is much more prevalent. The article though deals with the controversy and the history that went into the development of the trinity doctrine.