Misfire codes P0300, P0305

The truck had no real problems up until my wife stopped to put gas in the truck. She didn't fill it up all the way, and had driven about a mile. She called me at work, so it was kind of hard to diagnose it over the phone. She said it was "running rough" and had died on her. She basically limped back home, about 5 miles, and I started to look into it when I got home.

First thing I did was start it up to see what it was doing. It was really struggling to start, and when it did, I had to feather the gas pedal slightly to keep it running. When I tried to give it gas more aggressively, it would start to stall, and eventually shut off. Those were the symptoms, plus a P0300 code, random misfire. My first guess was the fuel pump, so instead of troubleshooting it, I set out to siphon gas out of the tank. I first used a hand pump which seemed to get out quite a bit, and I noticed that once it started getting closer to empty, the gas was looking worse. Had almost an opaque look, and at the time it didn't Dawn on me it was bad. I siphoned approximately 10 gallons out, and stupidly used that gas in my other truck. After driving the other truck a couple days, it got a P0307 code, and the light bulb went off in my head. Well, I removed the bad gas, put in good gas, reset the SES and that truck ended up fine. So, bad gas seemed to be the culprit.
Back to the truck listed above. Figuring it was bad gas, I changed the fuel filter, checked the spark plugs, and put in about 5 gallons of new gas, with Chevron fuel system cleaner. Went to start the truck up, and initially had a hard time starting, but after a few attempts, got it running to where it wasn't as bad as before. I let it run for a few minutes, and upped the RPM's and wouldn't you know it, check engine light came on. I continued running the engine, and the check engine light started flashing, so I shut it off. I expected to see the same P0300 code, but now, the only code was a P0305, Cylinder 5 misfire.
I siphoned gas out once more through the fuel pressure test port, and got it as empty as possible. I put in new gas with ISO-HEET, and checked the plugs again. They didn't look too bad, but I swapped #5 plug with # 6 plug, and same result. Swapped plug wires, same result. My wife, by now, was starting to get antsy, so she went and bought new AC DELCO plugs, new wires, new fuel filter and new ignition coil. Replaced all of those at her insistence, and repeated the process, but the plugs, especially the #5, looked pretty bad. All the plugs had a "rusty" look on the ground electrode, and #5 plug was black on electrode and insulator. Couldn't smell any odd things, so new spark plugs put in. After all that, still the same result, P0305 code. I've researched until my eyes are bleeding, and I've read about fuel pressure test, compression test, spark test, etc. Not sure what to do next, and I don't want to throw parts at it, but may have to if wife keeps bringing them home. I'm not a master mechanic, but I can do a lot of things with the right instructions. So just looking to get a little guidance, just not from the wrong people. Thank you.