Figures. Was running perfectly fine, on the way to work this morning, about halfway there, I notice it is starting to hesitate under load, but only around 25MPH. Keep driving, hesitation starts to get worse...up to 50MPH under acceleration I can feel it. ALMOST to work and it starts to smoke, only under load. By the time I'm at work, at idle, it's producing a nice cloud. Symptoms: White smoke. Doesn't smell like coolant, but I'm running only around 30% antifreeze, so perhaps it won't smell like coolant typically does. Smells like "normal" exhaust. Never noticed bubbles in the coolant previously. Cylinders 2 and 4 (at least) are dead. Pull plug wires while its running, neither affects idle quality. Nothing wrong with wires, and they are affixed to the cap fine. Idle is fairly good, but not as good as normal obviously. Check engine light came on once after I noticed this problem, then went off a few seconds later...I suspect it was the O2 sensor seeing a problem, but I haven't pulled codes yet. The engine sounds like a diesel, ONLY on that side. I am 99% sure that the sound is the rockers. The engine noise has always been louder than I am used to, but without the stock clutch fan, the engine bay is much quieter overall. I attributed the noise (present since initial firing on both sides, couldn't pinpoint even using a hose for a stethoscope) to the roller rockers and aftermarket roller lifters with the link bars, since it never got worse, and I had tightened up the rockers "just in case" after hearing the noise. I went 1/2 turn on the rockers when I assembled the engine, so when I tightened it, it's now at 3/4 of a turn. Engine has run great since I got a good MAF, but there were two things now looking back, that are probably clues. The temperature while cruising at the same speed, same load, fluctuates rapidly...gauge isn't accurate as far as numbers, but the temperature will climb, then drop down, and repeat about every 30 seconds. It's obvious that the thermostat is consistent, but that the engine temp is increasing then decreasing very quickly. At idle, it heats up what I would consider slowly...with electric fans, just have to wait until they turn on. The fan (primary) easily cools the engine down though once engine temp hits 220* (fan on temp) I also (still) have the heater hose hooked up to the wrong place (water pump) but I doubt that is the problem with the temp fluctuation...it simply isn't moving coolant through the heater core. I had an oil leak (missing fuel pump pushrod bolt) that I was tracking down. THOUGHT I saw a bubble pop in the oil that was sitting on the deck surface of the #2 cylinder. If the head gasket let go between the two cylinders, then that wouldn't make much sense. I can't even be sure the bubble I saw wasn't already there or was just caused from heat, but it was there nonetheless. I plan on checking the easy stuff first, although I know there is something serious here anyways...have to make sure the two plugs are good, and make sure they are getting spark. I will compare plugs 2/4 with 6/8, and maybe even #1, since the drivers side bank is running fine. One thing with headers, depending on construction, pulling a plug wire while it's running is painful to say the least, if not impossible. After I figure out if the plugs and wires are good, and getting spark, I am planning on pulling the valve cover. Just going to do a simple check of the rockers, see if anything obvious has happened which has caused the loud tapping noise. After that, will use the starter to turn the engine, and watch those two cylinders, see if the cam is flat. I've got just my tool box, so I am going to have to scrounge up some bad clothes even. No scanner, compression tester, etc. I'm expecting to see that the head gasket has failed, AND that I've either got a flat cam, or something happened with the rockers. Can't think of any other reason that it runs so poorly, two cylinders are dead, it's smoking, and it makes noise from the valve train. I guess this is more venting than anything...I can't think of anything else that could cause these issues. But if you think of something, let me know! Was supposed to drive it on a trip around the Western US, definitely not going to have time to fix this before then.