I think you must try abstinence. Stay a couple of days without touching your tool and it will be more responsive to mechanical stimulation. Apart from that, it is a psycological issue. But since i don't believe in psycological therapies (unless someone is really suffering) i suggest you to neglet maturbation.
My experience: my cock is uncut but not very sensitive. If i want someone playing with it i do it when my balls are full, otherwise i don't enjoy it.
My boyfriend has a broken frenulum, there's a whiter strip where it was the frenulum, and in facts he has no particular sensitivity there: nevertheless he can cum anytime, with condom too.
Hope that helps!