When I say rough I mean like bad 70s carbureted motor rough. I've never seen an injected motor this rough during warm up. On the coldest days, it can even die out on me. The problem has only popped up since temps have dropped into the low 30s here.
I changed my plugs and wires according to GM spec a few months back so they should be solid. Oil is good ... at least Oil Stop says it is. Everything else seems fine and it runs great once it's warm.