The slipper, in stock form, is decoupled because the inside slipper plate drives the front wheels only, and the outside slipper plate drives the rear wheels only.
That's where the problem lies. Associate tried using slipperpads with more surface area (HT pads) but if you wanted to run your slipper loose, it cooked the slipper, glazing the pads, melting the spur, and I seen a slipper spring turn blue. For some reason, they totally seemed to overlook the weight transfer on acceleration.
I came out with a clutch basket that allows you to add an extra slipper pad and disc to drive the rear wheels, and Mantisworx is selling fiberglass pads that don't glaze up like the stock pads.

Pinning the top shaft has been tried by quite a few people, and what it does is tie the two slipper plates back together. It provides the rear with two slipper plates it needs for acceleration, but now the front is tied to the rear, and can't spin at a slower speed when it needs to, like when it turns a corner.

Mantis has a third option, but it's not for sale yet, and besides, I already mentioned him already.