See you haven't played for long enough to know whether there's a place for you in teh guitar world or not. There is hope for you yet. Your practice so far has been quite casual and irregular. First thing you gotta sear in your mind about learning guitar is that it requires inordinate struggle, perseverance and self-discipline. It is not a pleasant journey. Half-hearted practice sessions here and there will get you nowhere. You must apply yourself, exert yourself regularly. I'm not saying you have to play for hours on end everyday. Play 30 mins, but do it everyday, with attention and determination.
It is good to be ambitious, but it's unwise to let it overwhelm a realistic attitude. I know you want to shred like Buckethead without going through the trials by fire that the learning process demands. I do too. But it's not gonna happen unless you are ready to gear up for the ride.
Sorry for the Yoda-esque lecture. I couldn't help.
So your lofty ambitions aside, start with the basics. Start slow. You said you can't alternate pick. I think that's a major reason why you are unable to break the speed-barrier. I'm sure there aren't many expert players who can play fast beyond a certain speed just down-picking. Alternate picking is the tool of trade of every shredder there ever has been.
I think you are trying to begin your alternate picking from a faster speed than you can hold at this point. It is frustrating to start every new technique from the ground up, but it's the only way. If 80 bpm is the fastest you can do without alternate picking, try dropping some bpms and find the right bpm where you CAN alternate pick comfortably. Gradually work up from there.
Don't doubt yourself. Achieving a decent enough alternate picking speed is not that difficult. You can do it with a little patience.