If you'd like better results with the new Auto-trace command, take these extra steps before running the command.
If you are trying to trace a part of a layer, first mask out the areas you do not intend to trace. This will increase tracing speed and avoid unwanted masks.
If you are using a channel to trace your masks, you may want to apply an effect, which increases the contrast of that channel like levels, channel mixer, or brightness/contrast.