[Ali Imran]

N u believe the Koran was sent by Gabril to Muh?

Yes, I believe that and we have all the records preserved. We know the names of the first generation of Hafiz (memorizers of the Quran) and the following 3 generations. We know their names, their families, their jobs, etc. We have extensive records, which gives us certainty in our faith.

As for the NT, we don't even know who wrote it, or who made the changes, or how many times it was changed. More importantly, Jesus wasn't God in the beginning but his status was elevated and eventually, he became God. How do we know that? Because of the many ecumenical councils held by the early Christians in the first century, and what was discussed by the councils.