All power windows seem to share a common ground... when you tested for power at each motor did you loop a test light between the two terminals in the connector? This will tell you if the motors are getting power AND ground.
Thing is, I can't tell from my alldata wiring diagram where the ground is located... The diagram does say "E" over the universal sign for ground, so maybe it's an engine ground. I would suggest checking all of your engine grounds, loosening and retightening all of them.
Edit, wait a sec...I think I'm reading it wrong, sorry I'm not familiar with these, I deal with GM wiring diagrams most of the time...