ok... I just put a new (stock) gm crate motor into my 87 blazer. It was running great for awhile and now runs ok when Its cold, but once it warms up it has a rough idle and bogs really bad off idle but picks up and takes off somewhere around 2k rpms. The old engine had been run with a blown head gasket for awhile, so I cleaned everything from the old engine before I put it on the new one as best as I could. So far I have the new engine, new cap/rotor/plugs/wires/o2 sensor. What do you guys think?