It is odd, but when climaxing for a BJ, the sensitivity is TOO much it feels like my PC muscle really tenses up, like some sort of shock reflex, and don't always get that full satisfying release.
Anyway, it doesn't make me prem ejac, in that regards i'm fine. I think maybe the recommendations to reduce your foreskin in order to desensitize, might not necessarily be at the heart of the issue. Just throwing it out there. Try 'stop-start' or a different position, or take your mind somewhere else to avoid cumming maybe. Also, do you orgasm at a normal rate when masterbating or is this also quick?