What was the New Testament written in?

Aramaic. The Aramaic copies (such as the Peshitta) are older than any greek. Additionally, the greek has many Aramaic Words that merely became transliterated from the Aramaic instead of translated. Such as "amen", "anathema", "halleluyah", etc. Lastly, the NT was written in Aramaic/Hebrew prose with several Hebrew Word "puns" that translate into terrible greek form.

Also, the Aramaic corrects some bad greek translations like instead of "a camel through the eye of a needle" it says "a rope through the eye of a needle"