the new plugs, look fine, i mean they are kinda black, but just within the bounds of normal.
the smoke is more of a grey. so a very light black... i know it isn't your usual oil, it isn't coolant... i would say its running rich.
From what I can tell the temp is fine... its been driving around for a while with no issues.. in heavy traffic...
i had a honda that we were working on that when you gave it too much gas, it would retard the timing some stupid amount to stay alive... nothing helped. new parts, advanced the timing the whole bit. we later found out that the compression was all kinds of fucked because the sleeves were warped. so pistons 1, 2, and 4 were ok, but piston 3 was horrible... that was throwing the computer off and in an atempt to stay alive, it retarded the timing...
from the way it sounds/acts, this seems to be very similar... i just don't know if this blazer is smart enough to do that. and since advanceing the timing helped alot, it has really thrown me off.
we also checked for the vacuum leak by taking a bottle of starter fluid and spraying it around... we didn't see it move and the rpms never changed...
i'm leaning towards compression issues... it does have alot of miles on it...