Lowbeam headlight on passenger side not working. Not bulb or fuse. Used test light and showing no power to bulb holder....?

Check your Light Relay. Your owners' manual should show you which relay it is. I believe GM splits the power to the left and right sides of the car in the Relay assembly. There should be a small box under the hood. You may just need to WD40 a corroded terminal and the Relay itself may be okay. Another thing you can try is clicking the Hazard switch several times. The Flash to Pass feature on the Turn Stalk works the high beam, but some of the headlight controls go through the Turn switch.

If all the above fail, try turning off the Autolamp feature and see if the Headlight switch will work on plain off and on like the old cars. It is good that you checked the wiring.

Check your ground wire - you can test it by using a length of 16 ga. wire. Ground wire to something like the alternator bracket by clamping with vice grips. Look on the bulb wire harness and put the other end of your test lead into the black wire terminal and try that. If it lights up then I would just clip the black wire from the harness a couple inches out and connect your test lead. If you have something else grounded to that bracket then strip more of your test lead , loosen the retaining bolt, install your lead and crank it down. Costing the wire ends with dielectric grease will help prevent corrosion from killing your new ground.
Hope this helps!