99 jimmy intermittent shifting problem

I have a 1999 jimmy 4.3 auto with a transmission problem. This happens usually after longer highway speed drives. when I come to a stop and start driving again it will shift into 2nd very hard and into 3rd a little hard and also if i then put it into reverse from a stop it slams really hard and again if i shift back into drive. When i notice the problem I can shut the truck off for a few seconds or so and then it shifts fine until i drive longer again. A diagnostic code comes up and i think its a general code, it says trans component slipping. Im thinking it is some kind of sensor or something since i can "reset" it by turning the ignition off. this has been going on for a couple years but i know how to deal with it and not drop the tranny.... yet. If you want more details or have questions about it that will help you help me just ask? Anyone see this before or have any ideas? Thanks!

Welcome to AF, this usually requires a trans special scan to look at the the pcs solenoid, a common isssue, the pcm boosts pressure to compensate for percieved or actual slippage.