car hesitates badly when engine reaches operating temperature?

My 1988 Sentra has a problem I can't figure out --car hesitates badly when engine reaches operating temperature. Car runs very rough-seems to be starved for fuel when appling medium pressure to accelerator pedal. Idles fine at all times, you can feather gas pedal to make car go but as soon as you apply too much gas engine bogs down and you have to shift gears to make car go faster, then runs fine in next higher gear until you give it too much gas again. Changed fuel filter,cleaned carburator, replaced several cracked vaccumn hoses