[Kosmickid]

I had quite a few issues with my kit too where the gearbox was binding in a couple of places.

1) Check the 3 long screws that go through the gearbox around the lay shaft spacer and bolt the motor plate down are not hitting the slipper disc. If tightened too far or not correctly installed with washers or orientated they can touch the disc and result in the whole thing binding up. In my case all 3 screws were protruding too far.

2) Check the Layshaft spacer. Mine had to be machined down a fraction as when the gearbox was tightened it would bind up again. Machining it down solved this issue.

I would remove the motor and check the gearbox by turning it by hand which should be easy. You can remove one thing at a time, Layshaft spacer, differential, gears to check what the issue is. It's a tedious job but you'll work it out I'm sure.
As I mentioned I had several quality control issues with my kit which were addressed by Durango with new parts. If you need me to talk you through anything just PM me. Good luck