It's been 5+ years since I last saw / worked on a Reflex DC.

It sounds to me like the creep speed on the direction switch is working ok but there is a lack of any throttle pedal input for traction.

I'd check the throttle pot values at the A5 card under the armrest.

Pin 910 - Wire number 29 should be +12 volts.
Pin 911 - Wire number 30 should be 0 volts.

Pin 601 - Wire number 50 is the input to the card, voltage should be variable depending on pedal position.

I remember on older smaller BT DC equipment we used to get an issue with the small roller wheel on the microswitch inside the throttle pedal unit, it used to get a flat spot on it & cause non traction issues - I cant remember if the DC Reflex has this exact same set up.