Is it my GTX or motor thats playing up?

[FifteenthNeo]

Just fitted a new GTX into my XX4 and have fitted, for the purpose of testing, a Reedy KR modified 12x1.

Anyway, after using the basic setup function all seemed well until I tried a test run. Any amount of throttle resulted in a slight twitch of the motor and all was dead.
But, if I give the buggy a slight push it takes off and runs fine. I took it outsdie and it was running well until I slowed to make a slight turn as I backed off the throttle to make a tight, slow turn and as I went to pull away from a virtual standstill again it just wouldnt move until I gave it another push.

My wiring seems fine, meshing is good, batteries are fully charged in both the buggy and transmitter. Transmission is free.

Anyone have any ideas? Motor or ESC or whatever?