It's not "fake," but 1500 years old puts it a good 500 years after Jesus's death, so it's not really reliable as a historical document. There are much older scriptures found that do say he was crucified, plus there are older scriptures that say heretical things modern Churches reject. Unfortunately for the Muslims who want to use this book as proof of Islam, it alsos contains things that contradict Islam, like the idea that there are 9 heavens, that God has a soul, and that Jesus permits the drinking of wine.