The plot thickens. First, I looked up the firing order and I was wrong. It goes:
1 2 3
4 5 6
As viewed from the front of the car. Makes sense, I guess. So the plug I thought was #1 was #4.
While I had the plugs out, I did a compression test on the engine. It was dead cold, probably 45 degrees. Compression varied from 197 to 220 psi, which: 1) Is pretty good numbers, maybe even a little high, and 2) Is OK relative to each other, would probably be closer numbers if it got the valves adjusted.
Put plugs and oil in it, took it for a 40-mile drive to get some supper. The car ran smooth until the first time I went WOT and crossed the 3k RPM threshold, then it started missing on a few cylinders. I held it WOT after that to see what would happen, and it fuel cut at 4k RPM. The CEL was blinking and since I had my scanner with me, I plugged it in. Misfire codes for cyls 5 and 6 plus a P0300 random misfire code. It now had a continuous misfire at all RPM's. I hit the clutch and coasted, shut it off. Started it back up. Misfire was gone as long as I didn't get up over that approx 2500-3k RPM magic number. Crossed the magic number and it started misfiring and then fuel cutting again. Pulled the codes again and this time it was cyls 4, 5, and 6 along with the random code.
So I think I have two separate issues here.
1) I believe the timing belt has jumped a tooth on the front bank. I can't think of any other reason to be getting misfires on only those 3 cylinders, especially with new plugs. Too coincidental to be coil packs. Those were also the original codes I pulled from it when I bought it, before clearing them and running stuff through the oil to try and clean the rings. I'm assuming the computer is either pulling fuel or timing from those 3 cylinders once the misfires start, and that each time you restart the engine it's resetting and trying normal fuel / timing again, which is why those cyls run OK until you get the RPM's up and it puts itself into limp mode.
2) I know my compression gauge is good, so I think I might have some carbon buildup in the chambers / piston tops which is raising compression. I definitely need to run a little water or something through it to get that out of there. If I was getting misfire codes on all cyls, I'd assume my entire problem was that, actually, and that it was detecting knock and pulling timing or fuel. Which it might be as well.
All in all, I was tickled pink to see some 'good' compression numbers. I think my problem is confined to the oil control rings, and I think I can get them cleaned up with some more diesel fuel or just hours on the engine once I can get the timing belt replaced.
If I don't find a jumped tooth on the belt, then I'll start to worry more.