Intermitant slugishness and stalling

I recently purchased a Suzuki 800 vx with 45,000 miles and I'm having a intermitant slugish problem. It starts off fine but when I get up to to 70mph and open it up it starts hesitating and starts backing down and does the little jerky thing. Them it sometimes like "clears" it out and picks up speed like it should. It's a intermitant problem and it only happens some days. When it get's really bad it'll loose acceleration and even slower speeds like 25mph and will slowly idle down on it's own and will die. After leaving it for 5 minutes or so it'll start back up and ride for a mile or so before doing the same thing. I'm stumped and had the carbs and the tank cleaned out last week and I'm still having the same problem.
I sure would appreitiate any ideas and tips you could give me. Thanks.