OT but need help -1998 Tranny Question/Problem

[Piston]

Do you have a Check engine light on? Blazer1970 is correct, If the pcm see's a significant problem with the transmission (something that will do damage) it signals full line pressure to all shifts and disables the Convertor Clutch. You'll notice if you pull over real quick and turn the key off, start it back up and drive off... it will shift normal until the problem comes back. That is, if there is a actual problem with the trans. If you try the key trick and it still shifts harsh w/no od then its possible you have internal trans problems. Usually an overheating transmission will be very sluggish and even slip when shifting.
Since this is OBDII, you wont be able to pull codes like it needs to be. Have someone with a scanner go into the transmission section and see what the problem is. Most of the time we've seen either the ground wire from the PCM (gm has a tsb on this) or the PWM soleniod/shift soleniod/tcc soleniod.