92 SLT Sounds Bad

Suddenly my 92 Yukon engine sounds like it is knocking even after warmup. Before my last oil change I began to notice this slightly and put some lifter additve in the new oil - seemed to take care of it. Now about a month and a half later it is back and starting to sound worse.
Any ideas; headers, lifters etc?

Thanks :mad:

Well, found out what was causing the knocking and it wasn't piston slap. The freakin crankshaft pulley had major play in it; wobbles from side to side! Damn, looks like I'm into a new engine. Oh well, I did pick the rig up for a decent price and the body and interior are in good shape. A couple grand for a new motor and it'll be almost like a new truck.
Anyone else ever seen a crankshaft just take a crap like this? I guess that's what I can expect from a GM product.
:frown: :frown: :frown: :frown: :banghead: