MTH PS-3 DDC speeds steps are in fact smph. I've done the math and confirmed it with a phone app. And it is my understanding you can't change the speed, only the rate at which the speed changes (Like Legacy momentum setting.).
Can confirm, the speed steps are accurate. Also, I highly recommend setting the "MTH Acceleration" and "MTH Deceleration" in CVs 53 and 54 to values much lower than the default. I use 24 for both, which gives very nice smooth start up and stopping.
https://www.mthtrains.com/site...ction/20dl19404i.pdf
I do not believe there is a way to use a custom speed table, however, without disabling the use of the tach feedback. CV52 must be set to enable "PWM Mode", which as far as I can tell makes the controller run completely open-loop. This is pretty much useless.
Also of interest may be the testing I did in this thread, regarding tach tape spacing. I do this mod on all my diesels, and the transformation in speed control is great. This, combined with the accel/decel tweaks, makes them almost as driveable as a Loksound.
https://ogrforum.ogaugerr.com/...g-how-low-can-you-go