Are you running 2S or 3S? Kind of doesn't matter... I ran 2S and those didn't last more than a bash or two before blowing one out, especially the rears. They just can't take the punishment that's asked of them.
I've read that the rustler 4x4 vxl has stronger ones... you can investigate that. I went with MIP X-Duty's. Expensive as all get out, but I haven't had any axle related issues in over a year and I started running 3S a month or so ago in it.
The slash 4x4 and stamped 4x4 use the same MIP x-duty axles. MIP just has 2 part numbers, in case your shopping and all you can find are slash ones.
Just checked my stampede photo's, it's almost been 2 years since I installed those. I had the truck for a month before getting them, if that's any indication as to the frustration level I was at already, just running 2S with traxxas chevron 2.8 tires (not very grippy).
The only issue with the MIP's is that the little grub screws that hold them onto the diffs like falling out, so it has to become SOP to check and tighten those before every bash and a good idea to do so whenever you switch out packs.
Just ran mine a couple weeks ago in the snow, quite a few different things on it since the above photo, but still rocking the MIP's:
Can really be made to be a tough little truck. I launch this thing like I do my outcast. Takes a bit of $, but it is fun.