Hobbywing bec issue?

[OneKiwi]

I have in my box a HW 120A V2.0 esc

The esc works well BUT when it (the buggy) is at speed there isn't enough power going to the servo and it doesn't turn nearly at all. When im not on the gas its fine or if I hold it off the ground and turn the wheels its fine. Only on power

Is there a fix or something I could do besides plugging in a life battery pack to the receiver?

Thanks