Re: Excessive gum bleeding around crown....
Was the dentist who checked the root canal an endondontist? - if not I would go to one and have him evaluate the tooth - it can be a deep seated infection at the very tip of the root which can sometimes be hard to detect by the untrained eye of a general or cosmetic dentist. If it checks out OK with the endo, discuss with him what your next steps should - he should be able to rule out a fracture of the tooth below the gum line as well so there should be no need to go see an oral surgeon but he might refer you to perio if he notices signs of periodontal disease such as an infected pocket around the tooth or bone loss,etc.
If none of this works and the source of this still can not be determined I would suggest the dentist remove the perm crown and put a temp crown in place with no metal fused to it and let you wear the temp crown for several months to see if this will clear up on its own given a different "environment" - it can be anything from a a reaction to the metal fused to the crown, reaction to the cement, deeply seated margin of the crown or its too high so you are biting too forcefully on it, etc.