I had this same issue with my Bomber with the exact same setup. Buttery smooth in reverse and cogging like a mofo crawling forward? I figured out the sensored motors don't like to run in reverse efficiently with the MMX for some reason?!? So I flipped my ring gears around front and rear to correct the motor direction to normal instead of reverse and bam, no more cogging!!! :-)
This issue should be fixed with the latest firmware versions. There was bug in version 1.77 that when you put it in reverse mode it was still expecting the sensors to trigger in the same order as spinning forward. We are making more improvements to sensored running and should be releasing a new firmware in the coming weeks.
