And your problem may not be in the tx or ICE.
If the motor isn't going any faster past a certain point, it could be your pack is not up to the job. Using your meter, watch it while advancing the throttle. If it gets to the point where the motor isn't increasing, be willing to bet your pack readings are maxed, and any more throttle will show a steady or dropping reading.
The motor wants more to do more, and if the pack isn't able to deliver the power, it will only go to a certain point before demand exceeds supply.