I replaced the scored Miche headset on a new-to-me 1998 Peugeot Competition CP20 frame with a Campagnolo Record headset, and now that I've got the bike built up the steering is stiff and lurching when I get to the sweet spot of tightness on the threaded race. Actually, it keeps lurching when I purposely loosen the race, as well.

Any idea what this could be? I've got the ball retainers on properly (double checked that), so that's not it. I lathered the top of the balls with grease, but not the underside of the retainer. That wouldn't be the reason, would it?