Bummer, man. I have heard about this premature ejaculation stuff. First step is to admit you have a problem.
40 is a whole lot longer than average, but not in the realm of legend. When I was younger and on a one night stand quest, I never ever went less than an hour. My theory was if the girl was talking to her freinds about this animal who went for 2+ hours then I had a better chance bagging the friend too.
It has never been dificult for me to go a long time. Just have to have good control over your own body. Don't get too excited, and act as if you have been there before, and you can pretty much go as long as you want to.
Are you guys that are lasting ungodly amounts of time using condoms. I could see lasting that long due to condoms since I can't feel a damn thing. It's also been 3 years since I've used one so it would be pointless to try and use one now.