Gnosticism

>what do you think about Gnosticism being pejoratively associated with Narcissism and New Age spirituality?

by whom? Gnosticism is just early Christianity with a heavy Greek slant

Mostly blavatsly influence groups. Most new agers are pseudo Hindu now as far as I can tell, or neo pagan

What is it called if you are absolutely certain that god exists and that we each have an immortal soul but are equally certain that all religions are false and worthless?

Undefined theist?
Could call yourself and theo-immortalist to get the immortal soul part in.

Immortheist to up the Latin aspect

Theo-Immortalis
This would mean immortality is the gift of god

How are you certain god exists without having any ideas about the nature of this god?
How are you able to be certain that he is the only god?

Through Gnostic experience, duh. Read the room

This. I like that Gnostics have no priesthood and therefore no dogma.

which is why they're extinct lol

Han Jonas' work discusses the "alienation" within Gnosticism and how it differentiates Gnosticism from other religions - an echo to your argument.

Furthermore, the platonic and neoplatonic relationships with Gnosticism are well documented, so I can see how Bloom could land on Gnosticism as "the religion of literature".

Making the distinctions are important to me because my principal interest in Gnosticism is historical - specifically the Syrian-Egyptian branch. Without the context of Bloom's quote (with his work I am not familiar), my impression is of a Gnostic in the Western Occultism/Esoteric tradition or a "Gnostic" like Jung rather than historical 3rd century Gnostic.

That great enlightenment ideal: Deism.