So... When the wheels are in the air there is no slipping for my slash 4x4. When in the ground, there is the sound of gears slipping, but on close inspection in the video below the sound only comes when the rear wheels are not moving.
This had happened before and I changed out the diff gears (internal, I think they are called spider gears?). The teeth on the spur, ring, and pinion are fine, and the driveshaft set screws were tight.
On changing it it was fine on the next run, for one pack then the slipping sound came back.
Would appreciate any help. as you can see the front is fine. So shouldn't be spur or pinion or center driveshaft.