My cousins sammi had the same problem. Ran great for awhile, until you were trying to climb a hill then started cutting out. You could change the fuel filter and it would run great for a little while, then start doing the same thing. His gas tank was dirty, ended up having to drop the tank and have it boiled out.
Sounds like you need to do the same.
Also, check all your fuel lines for cracks. Thinking back on his problem now, I remember he had an electric fuel pump installed under the hood next to the battery. The rubber lines coming in and out of the fuel pump were rotten, and were squirting fuel out when you really got on the throttle. Start at the carb and work your way back to the tank, replace any line that looks suspect.