I'm having the same issues. only in 1st and only once it is warmed up. if it's cold there's no slippage. when it's warm it's like having a 4000 stall "strip" torque converter in it, unless you baby it OR if i pull it into 1st gear and shift manually it won't slip.
this problem is not the axles. if the problem was shudder only, I would side with y'all.