I had the same kind of issue with a bow a couple years ago. As it turned out, my bow was just not a good bow. Not necessarily the the brand or model, I just had a bumb bow. I couldn't shoot past 40 yards to save my life, and even that was touch and go. Bought a new bow, and right out of the gates could shoot 60 yards without a problem, and have never had that problem since. Right now, my max range, keeping all arrows within an 8 inch pie plate, is 100 yards. I don't hunt at that distance, but practice there.
Theres really only two things that would go wrong: your equipment, or your shooting form. My first step would be to rule out an equipment failure. Find someone who can shoot great with their own equipment, and take the time to have your bow set up for your buddy. Let your buddy shoot it, and if he has the same issues, then you know there's an equipment failure. If your buddy shoots it just fine, then you know the problem is shooter error. There are a thousand things that can go wrong with a shooter's form, so if it's shooter error, that can be a process. But, you can't fight the problem if you dont know with side to attack. That's my suggestion, someone may have an easier one, but it's what I would do. In fact, I have done that in the past with my brother, because he was having issues with his bow. Turned out that time that he just needed to adjust his form. Hiccups in your form can be very easily covered up or missed at 30 yards or less, then take a dramatic leap just 10 yards later, so consider everything, and good luck.