OK, I give up. According to the review in MR when this 2-6-0 came out, its minimum speed on straight DC was 5smph. I've got 2 of them that I'd never used and neither one will do less than 10smph without cogging. Pulse doesn't help much if at all. I'm running with an MRC Tech II powerpack.
I took one of them apart, cleaned and relubed it, adjusted the gear teeth clearance, and it runs no better than the one I didn't touch.
I did note a slight hesitation when the main rod and side rods are both horizontal on the right side, but I can see no cause for this other than a general sloppiness of fit. I'll remove the rods next and see what happens, but of course I don't think that'll help the cogging.
Have others had the same experience that I have or do your Moguls run at the 5smph that MR claimed for theirs?