Stalling/Chuggin Problem

[Sylvia]

So basically when i start it up its fine. it idles at about 1000 but when i rev up to about 6000 rpm and let off it will go down to about 3/400 and almost stall and start chuggin but after about 2-3 seconds will go back to idle. If any has any idea whats goin on please post. Thanks.