just set up dcs for the first time

I don't know DCS like I know TMCC, but as the signal comes in through the pickup rollers, which makes DCS a bit more sensitive to dirty track, I'd investigate those spots first. Or so I understand. 

Bill,

Almost certainly the problem isn’t dirty anything and has nothing to do with the DCS sIgnal strength  or lack thereof. DCS engines that lose the DCS signal keep doing whatever was their last command and DCS doesn’t issue any commands spontaneously.

It’s most likely related to either the tach reader distance from the stripes on the flywheel, the state of the stripes or the tach reader itself.

if it happens in the same "few spots', the track might be involved.

Is the engine steam or diesel?  Model # helps.  One of two major things.  Either this is track voltage related in that those sections of track have low voltage due to a bad connection and the engine is seeing variable voltage and speeding up to compensate an then slowing back down when the voltage rises again.

Or and more likely you have a steam engine and the tether has a bad connection or broken wire and you lose tach signal in curves.

If a diesel or only in straights, it is track work or potentially what Barry is stating.  G

Thanks for the info.  I dropped a couple of feeder wires and really cleaned the track with a track cleaning pad. The problem seems to have gone away.  Thanks again.