need help troubleshooting

I have a recently rebuilt (2000 miles ago) LS5 71 chevelle that has started smoking out the drivers side. The odd thing is it only smokes when at a dead stop. My friend followed me to a car show saturday. We drove 60 miles and never came to a complete stop until we arrived at the event. It never smoked along the way as we passed through many small towns, rolled all the lights and stop signs, went through the gears many times and the entire RPM range but nothing above 3000 rpm. I have been told the valve guides or rings may be the problem. Any help would be appreciated.