Dang I wish I saw this thread before you sent it to the stealership. I cannot explain why, but in the days of past on Chevy Small and Big Blocks the damn oil pickup tube was held on my maybe one bolt if not two! Either way we would tack weld the bitch to the block as well as the pickup tube to the pump since it was a press fit. Numerous buddies that race had issues with the bolt backing off and falling into the pan. Oil pressure would be fine until you were at the end of the track and made the return to come back to pit. Guys would say " my oil pressure dropped after the run when I made the return road." It got to the point where we could laugh about it when it happened to other friends because we knew exactly what happened. When either the bolt or pick up tube comes loose on those motors it will literally swing when you make a turn, exposing the pickup to air and oil pressure instantly drop. This has happened too many times for me to count in my youg age. Needless to say it's practice now to tack the bolt and tack the pickup to the pump. Maybe high rpm vibration did the same to your 10.
Since you changed your own oil I would have recommended draining the oil, and getting a cheap scope from a plumber, Harbor Freight or Sears for minimum price to see yourself through the drain hole. Those pencil LED lights work great as well. You can't make the reapir that way, but at least know what the problem is and where in sam hell the bolt came from.
Best of luck bud!