hesitation

[tdach]

Hi
I've got a 13.5 thunder power motor connected to a hobbywing 1s esc.
Halfway through a heat it started hesitating on the throttle. On the bench when I apply full throttle it runs at half rpm for half a second then steps up to full.
It still drives, and if I can keep the car rolling I don't even notice but coming out of tight hairpins or if I stop for any reason I get this hesitation.

I tried a different sensor cable in case it was that. Tried a different battery in case it was a voltage isue and I've been over all my soldered joints and can't see anything obvious.

If anyone has any ideas I'd appreciate some help?