Not familiar with your particular ESC but I would start at the beginning
Centre throttle trim
Set throttle travel (EPA's) at 100%
Calibrate ESC
Sit car on flat surface
Adjust thottle trim until car starts to move, then back it off slightly
If steering affects your throttle then you may have other issues
What steering servo are you using ?
Your RX might be browning out (losing signal) usually caused by a weak ESC bec
Limit your steering servo travel and see if the problem goes away
You may need a glitch buster style capacitor or external bec
Cheers