Pcs

Just wondering how hard it is to change a PCS in a 99 venture and where would i start to find it. The transmission is hard shifting and and there is a
whinning noise coming from the motor and I can shut the van off for a while and it must reset because it is fine again until the next time it wants to mees
up. Thanks for your help.

There are a great many threads about PCS across GM lines on AF. Enter PCS in the Google AF search engine.
Here is one exemple:
http://www.automotiveforums.com/vbulletin/t670085.html