WHi Bill,all,

>>Whenever my locomotive starts to stutter around the track I find the performance is immediately cleared up with a general track cleaning (LifeLike cleaner and Q-tip). My question is....is the traction tire the main thing that leaves the black residue on the track? Do I have to clean, somehow, the center stud system too, or just the outside rails?<<

You can also use isopropyl alcohol to clean your tracks.The traction tires are not the main culprit that get your track dirty.Just general dirt in the air falls on the tracks,and oil from loks of car wheels deposit on the tracks and really attracts dirt!
Herkat,LUX make track cleaning cars that will make the job easier.
The center studs are self-cleaning in a way,by running your trains.Some have devised a boxcar(with a pickup shoe) and very fine sand paper glued to it to clean the 3rd rail.

Kevin!