When you're in open loop it doesn't trim short term (INT) or long term (BLM) it just runs off your VE (Volumetric Efficiency) table. Once it goes into CL it will try to trim your INT & BLM. If it shows a BLM of 100 it thinks you're running rich. It may be rich or something else is fooling it like ignition issues, it can't trim out mechanical issues.
What brand distributor did you use, an ACDelco? What about the coil, when did you replace it? Take a spray bottle of water and spray the coil while idling (just the body of the coil not the wires), see if it runs worse. A shorted coil may take out the ICM in the distributor too. I had this happen to me recently, ICM fixed the surging while cruising and cap and rotor helped idle some but it still stumbled, coil fixed that.