I read this thread when I had the same issue. I've had a dozen or so Sportsters over the years and had just about every problem it's possible to get, but this low rev hesitation had me puzzled. It was like almost stalling in traffic and took a few blips to get it back to fast turnover. I re-jetted, tested the reg-rec, swapped the coil and in desperation put a new carb on - but all to no avail. Took it to the local guru and he scratched his beard and said, 'Hmm... maybe the crank sensor..?' And yes it was! An easy fix, thankfully. Now the bike picks up easy from virtually zero revs, it doesn't kangaroo through the low rev range and it's a pleasure to ride again. Hope this helps.