If the mullahs have lost faith and trust in the military (especially the iRGC)- then a precursor of a coup has already occurred. The military has lost its loyalty to the regime. The breakout will be when the regime can no longer contain an untrustworthy military by confinement and purges of its leadership.
The mullah’s managed to break and take control of the power of the shah’s military and has spent 30 years building a parallel (but now more powerful?) ideologically driven Rev Guard counterforce.
So if they lose confidence in large parts of the IRGC - what next? We don’t hear much about what is happening out in the provinces, beyond the cities, in the small villages that provide the peasant manpower for the paramilitary.
When the military and police turn against the regime and attack the outside thugs, things will get really hairy there. THE ONE will probably go on another date with Aunt Esther.
The trick in any dictatorship is to keep competing interest groups at war with eachother, while preventing any single group from getting too strong. If the IRGC actually thought of itself as stronger than the Iranian military, that could be a bad thing for the dictator Khameni. You only want the IRGC “just strong enough” to deter the military from taking matters into its own hands.