Trim the silver skin from the pork tenderloins, if necessary.
Add the garlic, cumin, chili powder, smoked paprika, salt and pepper to a small bowl and stir together until combined.
Coat the pork in the spice mixture and use your hands to rub it in.
In a large measuring cup, whisk together the maple syrup, broth, mustard and vinegar.
Place the tenderloins in the crockpot and add the chopped onion.
Pour the maple syrup mixture over the pork tenderloins and onion.
Slow cook on high for 3 - 3.5 hours, or until the pork has reached 160F degrees and can pull apart easily.
Transfer tenderloins to a cutting board and use two forks to shred them apart. Place them back in the slow cooker liquid and mix around. Keep warm until ready to serve.
Notes
Make sure your pork tenderloins are roughly the same size so they cook at the same rate.
My pork tenderloins were 1.5 pounds. Smaller ones may cook a little faster.
For smaller shreds of pork, cut your tenderloins into chunks before cooking. This may also speed up the cooking time.
If the pork doesn't shred easily, I recommend cooking it a little longer.