Motor jitters in reverse.

[Moss Models]

Any help with this will be welcome.

ESC is an ORCA VC4 Pro 2 and motor is a Speed passion 21t stock brushless.

The problem is when running in reverse the motor turns very slowly and just jitters with not enough power to move the car backwards.

Just before we all state the obvious you can discount the following.

Transmitter does not have ABS
Tried reversing transmitter and still does it.
Been through all settings on program card with no effect.
Runs forward just fine.
Checked all end points ect. ect.

Has anyone ever had this?

Thanks