My experience backs up Jeff's advice. Buy a Lyen. Two GM MP3 controllers failed with very few hours (minutes, really) on them. My Lyen has close to a hundred hours dragging 400 lbs around.
It is a shame such nice design work is being screwed over the by the low assembly quality and component penny pinching I saw in my two failed GM controllers. Just as an example, the controller is to be used with a 57-58 volt fully charged battery, and the capacitors are only rated for 60 volts. That is just dumb, and the layout tells me the designers were not dumb.
That said, I don't understand how the controller can work only in Regen. The output FETs have to be sequenced properly for regen to work, and they should then also drive the motor. Did you try disconnecting your brake connectors? If one of the brake switches is on, the motor wont drive, but the regen would still work. I fell for that..........
TTFN,
Dennis
Ps MR Lyen is easy to work with, too. And he answers his email.