Have no idea what a GD is however if it has a manual gearbox some of these have a neutral switch on them .
Mostly these are wired into the cranking circuit so you can not start the mower in gear which puts too much load on the starter.
Does it die before you take your foot off the brake / clutch pedal or after.
Sit on the mower , with it in neutral and try to engage the blades.
Let us know if that also kills the engine.