Trench engine starting and stopping

[p51]

I have a trench engine 2-6-2T and thought I'd broken it in. But every now and then, it'll just stop for a moment, and sometimes the sound will just keep cranking along. The longer I run the thing, the more unreliable it is when I run it.
It's not dirty or poor connectivity track work, and it doesn't happen all the time. I looked at the wheels and they don't seem dirty.
It's always been iffy going over unpowered frogs, as if the 'keep alive' inside it doesn't know it should still be cranking past that. Bit again, sometimes it works well, other times, not so much.
Anyone seen this problem before?
I'd thought it would get better over time, but to be honest, it is becoming by far my most unreliable engine (as I only have the Whitcomb 50-tonner and the rest are the ten-wheelers, all with long footprints for contact and smooth running out of the box).
I'm starting to regret the good review I gave of it in O Gauge Railroading magazine at this point, even though the review paid for the locomotive and the details parts I put on it...