I may have figured it out....
As I posted earlier, my 98 4.2L was suffering from hesistation and bucking. I replaced the plugs and wires earlier, but was never really able to get rid of the problem. Last night, on my way home, I was stuck behind a slow moving vehicle and got in the situation where I either had to run in fourth gear and run the RPM's up a bit, or lug the engine a bit in fifth. Either way, higher RPM's or lugging is what causes the engine to buck.
At this point the hesistation and bucking started again, and then it progressed all the way to a dead miss in the engine (never done this before). when I got home, I popped the hood with the engine limping along and was greeted with a light and sound show. 1 of the plugs was arcing out on the block (hence the dead miss) and 3 more plugs actually had blue glows right above the base of the plug.
Come to find out, the plug that was arcing was cracked and the other three plugs had grooves burnt into the porcelin of the plug running from the tip of the plug to the base where it was glowing blue.
I have NEVER seen this happen before. I replaced the plugs in the truck about 30,000 miles ago, and the plug wires about 15,000 miles ago. As far as I can tell, either the plug wires went bad first and starting arcing out and grooved out the plugs porcelin, or something was wrong with the plugs, and ended up destroying the wires.
When I pulled these plugs today, I noticed also that the porcelin had also started flaking off. Almost like they all had gotten extremely hot (even though the engine has never been ran hot). At first I thought it was the old silicone boot grease drying out, but after cleaning off the old plugs you can see where the glass had begun to flake off. Really strange.
Anyhow, I decided to stay away from these plugs again (Bosch Plats) and ended up going back to the old faithful plugs, Autolite Plats. I also noticed when I put the autolites in, they fit in the boots of the plug wires much tighter than the Bosch plugs ever did. The Bosch plugs were the correct plug for the truck, I checked again today to make sure.
The truck runs great now. I have put slightly over 100 miles on it today trying to make it hesistate and buck. I have ran the engine up high and lugged it down to the point of almost stalling it and cannot get any bucking out of it.
maybe this did it. I guess I should have replaced the plugs and wires together (even though the plugs only had 15k on them at the time). Another thing I noticed, the Bosch plats had actually lost their gaps in 30,000 miles. And I know that the gap was correct when I installed them cause I indexed the SOB's.
Oh well...hopefully this fix will stay fixed for a while. 80,000 miles and counting. Too bad this didn't fix my door cracks as well!