Shu! look great bro! im looking forward to seeing it in real life. As to that twitching thing, it could possibly be a calibration issue. it might be that your remote is just on the edge of the minimum ppm that your sabretooth is expecting for a move stimulus, this will intern give the motor a really low pwm, to low to exceed stall under a load.

Somethings you can try: are you able to change the trims on your pot? Do you have another remote that you can link your bot to and try to recreate the same effect?