1999 Chevy suburban 1500 5.7 rwd. The truck just had power steering pump replaced and while it's sitting parked, after a few minutes the steering wheel full turns to the right or left,until I stop it or it stops itself. I have never seen this before. I am loosing my mind.

 

Sounds like you have a stuck PS valve. I run full-synthetic fluid in my 98" Chevy K-1500 and have never had an issue with it.

 

+1 sounds like worn spool valve in either the rack or box

 

I have a video of it but don't know how to upload it,to this site.