1996 Gmc Jimmy Seems Drive Almost Fine Slow 0 10mph Try Faster Gives Hard

it seems to drive almost fine when going slow (0-10mph). when i try to go any faster, it gives a hard time. i'll be giving it gas and it doesn't want to grab any gears. the rpms will get high and have to keep them high in order to get it up to speed. after awhile it'll finally grab a gear but sometimes it'll fluctuate as in it'll continually go in and out of how it should be. i tried to shift it down from overdrive to drive then 2nd then 1st but it doesn't make any change at all in how it acts. acts still exactly the same in 2nd n 1st like they don't exist. and if i am sitting at a stop sign or light for a few minutes, it will sometimes stall out.