Yep, the rings didn't seat. Warm it up, and run it at 2500 RPM for a while, it will probably make visible smoke then. Or run it at highway speeds, then let of the gas until you are down to 30 or so. Boot the gas and watch out back, a big puff of smoke means bad rings. Either live with it, or re-ring it and break it in right. BTW, what oil are you running? Synthetics won't let the rings seat. Break-in should always be done on dinosaur lube.