i think i might know whats wrong with it mine did the same thing!
when i cleaned my carb i did not remove the jet nozzle come to findout i had crap blocking 4 of the 8 holes in the nozzle.no mid and high revs just boged out ran like crap.
(even backfired a few times in mid)
try cleaning the nozzle
take your main jet out,now where the main jet screws into the carb is the main jet nozzle,set your carb on your work bench with it upside down (float side up in the air)(throttle slide flat on a towel) and take a drill bit to drive the nozzle out of the carb from the float side.(pick a big enough bit to not messup the jet threads in the nozzle)
once you get it out you will see 8 tiny holes in it make sure they are clean spray breakleen through it till all 8 holes spray good.
spray the ports out to
my 98 had this same symptom and it had junk in the main nozzle it fixed it
did you clean and check this when you cleaned your carb?