I had a similar issue making a crab, and I think I fixed it by double-checking and making sure that the StartOffsets for LStandLimbPath and RStandLimbPath were equivalent to each other (eg in my case x=-1, y=9 and x=1, y=9 respectively.)

It may have also been the LWalkLimbPath/RWalkLimbPath StartOffset instead, but I'm pretty sure one or the other of the StartOffsets fixed it for me. Basically Y the same but X opposite.

Of course if your legs are asymmetrical it's going to be a bit harder, and you'll probably have to have different limbpaths for each leg.

I'm not sure if this will help you, but I saw this thread a lot of time ago.

Did you use your own walkpaths for the ACrab?

And if you ask anyone that has made "unique" crabs?

Like, Major did one for the ERS mod which was a huge walking tank, I suppose he made the walkpaths himself. Why don't you ask him?

I'll try to fix it if you don't mind PMing the mod to me.

The floating has to do either with the foot atomgroups or the offsets of the legs. I don't deal with ACrabs too often but the shakiness might due to a low WalkPathStrength or it's center of gravity isn't low enough, or its just because the ACrab is too big.