Did you calibrate the ESC? Also check the instructions to see if they require you to reverse the direction of your throttle on the Tx, then re-calibrate if necessary. Steering going out could also be caused from a brown out... is it cutting off when steering full lock or only when going straight? Maybe check the EPA is properly set for steering too so no excessive binding on the servo at full lock. Did you gear down with the higher kV motor? Could be drawing too much current from the ESC, was it a matched combo or did you randomly select the electronics?