I'm only adding one cent here and I only glanced over your issue.
Obviously there are factors that change what the board can do. If you ran at lower track voltage for example, or if something isn't providing full power to the board, I'd guess that would seem like the board would handle less.
I believe these PS3 boards handle good loads. I have them in other brand one gauge engines that are power hogs without issue.
I had a one gauge engine that had a power path burn out. It was a printed circuit board that carried power from wheel pickups and the actual printed path was burned so that was one less point of power. That engine did not run right until I fixed it.
Of course none of this may apply, I'm only throwing something at you to consider looking at everything.
I've seen MTH board equipped engines stall because the tach didn't get the expected response from the motors. I've had chaffed wires rubbing the frames. Even a missing insulator inside a truck power point causing havoc. An old PS1 Allegheny I upgraded, had an intermittent short from a protrusion touching a smoke unit power pad. Took me near a year to finally find that one. It only occurred on certain turns or shell twists.
I will watch this thread and try to stay out of the way. Good luck and I will try and help with the little I can add.
