Suburban :: Car Misfire After Working On Engine

I replaced the oil pressure switch on an '07 Suburban 5.3L because the oil pressure was showing low once the engine warmed up. That did nothing, then I found out about that little filter/screen under the sensor. I intended to remove and clean the filter then reinstall it. While I was pulling it out, I dropped it back behind the engine and couldn't find it. I checked online and found a few people in other forums that said to just remove the screen as a "fix", so I left it out and put the sensor back in, just to get the vehicle drivable. It started right up and ran fine for me, parked it, and a after sitting for a few hours it started popping while driving with the SES light flashing on the drive home.

Code P0300 was set, no cylinder specific misfire codes were present. I checked the misfire data and cylinder #6 showed tens of thousands of misfires, #5 showed several hundred, but I think it was just picking them up from #6 since #5 is right after #6 in the firing order. I disabled each injector with a scan tool, all changed the idle except #6, it did absolutely nothing. #6 fuel injector had good pulse to it, I connected a fuel pressure gauge and put power/ground to injectors #6 and #4, both dropped the same fuel pressure. I did the "cylinder deactivation" test on the scan tool for the four cylinders that have it, they all did the exact same thing - the engine bogged way down for a couple seconds and then died. Is that normal? I can't say I've ever seen a V8 engine die before when running on 6 or 7 cylinders.

I checked compression on cylinder #6, it showed very low, almost zero, but I tried it a few times and it would show just a little compression at times... valves staying shut? I'm thinking when I opened the pressure relief valve on the gauge and the piston was near the bottom of the cylinder may be when it showed some compression. I also switched the coil/wire/plug from #6 to other cylinders and the miss did not follow.