So I'm with the NCR and have the "Soft Hearted Devil" fame rating.
I am wearing Tesla Armor. I have Boone as a follower and I have recruited the Great Khans the BoS, the Boomers and the Enclave. I killed Caesar and saved President Kimball.

So I am going through the "Eureka Quest" (Hoover Damn) and suddenly all the factions I allied with randomly start firing at me. WTF is going on? Frankly, i'm really pissed off at the unstable game.

Did you wear faction armor and put it in a container when you were still wearing it? Or did you use it for repairs?
If so, the game might still think you are wearing faction armor. To fix these bugs you must find another set of
the faction armor and equip/unequip it. I don't know if these bugs were fixed with the last patch. It might also
be the tesla armor, as when/if the NCR finds out that Arcade used to be with the Enclave, he won't get the nicest
treatment, either.

I wore Arcade's Tesla Armor for the whole final quest playing for Yes Man (not even NCR, though they Idolized me) and the NCR never fired on me.