boy I wish I saw this post sooner, I had the same problem on my 97 LS with a 3.5L engine. one of my ignition power coils (controls 2 cylinders) has a small crack in it and sometimes malfunctions. when it does, it only does it for a slight while and then goes away, its only done it twice since I owned the truck and haven't really replaced it b/c it almost never posed an issue. however the two times it did act up, it caused the check engine light to come on and the code when read said missing cylinder(s). it had the same symptoms you were talking about, vibrations, loss of power, and sick running sounds. I would also check out your plugs and wires and a good tune up, lifter tick I wouldn't worry about, like mentioned, its not a big deal and is common in these mitsu engines. I actually think it sounds kinda cool.