You can check to see if the signal is a problem by performing the coin test on the track to see if the breaker will trip in the DCC system. This seems doubtful since it hasn't always been giving you trouble. Of course, if you lost a solder joint, for example, the feeders could be a source of trouble, as Lee suggested.
I would still look to the track as the cause of the problem, though, especially if the problem is occurring only in certain spots with multiple locomotives. On my layout, I developed stalling at the turnouts and ended up powering my frogs, because I think that it's asking a lot for the switchpoints (which receive power through contact with the stock rails or some other contacts) to cover for the unpowered frog. On my four-axle units on Atlas #5 code 55 switches, it works out that one truck is on the points and the other truck is on the frog. That can be a recipe for stalling, if the frogs are left unpowered.
Hope this helps,
Dave Foxx