I wanted to update this to possibly help others who might have the same problem. The suction air leak was somewhere between the threaded inlet connection on the pump, the jandy valve controlling suction power from the skimmer and wall vacuum, or one of the PVC joints around the jandy valve.
After exhausting my efforts and replacing every o ring and gasket I could think of, I decided I might as well replace the jandy valve and PVC going into the pump. I figured if I call a guy to come out, that will cost as much as just doing this replacement and on top of his fee I would still have to pay to fix the issue. I had tried the shaving cream, soap suds, and smoke from incense tricks at all of these connections and even had a second pair of eyes from my brother-in-law and neither of us saw any reaction whatsoever on any of the connections.
I jerry rigged up a hose to 2 inch male screw PVC adapter to run water from the skimmer to the pump with the pump off and saw no leaks anywhere doing that either. So, all the tests and things you can try to do were ineffective at showing me exactly where the suction leak was. But, since they are so rarely underground leaks and this was the only area of plumbing that has been untouched in who knows how long, I decided it was worth it to replace it.
I do have the tiniest bit of air coming into my system from my leaf canister basket on my pool vacuum, so I'm replacing the o-ring in the canister as well, but the whooshing is gone and the pump holds prime when turned off now.