Remove the stems off the chiles.
Cut lengthwise and remove the seeds.
Place in a stock pot and cover with 2 cups of water.
Bring to a boil. Then turn off the heat.
Let sit for 5 minutes, or until pliable.
Discard the water.
Place the rehydrated chiles, salt, onion, garlic, cumin, and 2 cups water in a blender.
Blend until smooth.
Strain the sauce.
Rinse the pork and place in the slow cooker.
Cover with the guajillo sauce.
Cook on low for 4 hours on high, or 8 hours on low.
Remove the pork and shred.
Chop meat up if necessary.
Line a sheet pan with foil paper.
Brush oil on the foil paper.
Add shredded pork.
Place the pan under the broiler for 7 minutes.
Take out of the oven and toss the pork around using a spatula.
Return the pan under the broiler for an additional 7 minutes, or until crispy.
Heat tortillas and add pork filling.
Serve with salsa and enjoy.