1986 Sprint 340......weird problem

I have a 1986 polaris sprint and its having some odd problems. It starts and runs fine, but some times when you give it gas, it just stays at 4000 rpm's and wants to bog and not move. Other times, you give it gas and she runs and drives fine. Also, sometimes when it bogs, it will idle down really low, to about 500 and just stay there. If it bogs, you have to lift the rear end up and rev it up to about 5 thousand and jump on and go and it will be fine and then eventully do it again. Any ideas on what could be causing this? The sled is basically MINT and has way under 2000 miles and was taken into the dealer every year for a tuneup and everything.
Oh, and I have removed and cleaned the carb jets put in new pulse line and filter and have rebuilt the fuel pump.........for some reason I am thinking the fuel pump is still the culprit as it seems to me that it just isn't getting fuel at full throttle????

Thanks for any help on this!

1986 Sprint 340......weird problem