Sprinkle the pork on all sides with salt and pepper.
To a slow cooker, add the pork (fat side up).
Turn the slow cooker on to the 6-hour setting, and cover with the lid.
Carefully remove the meat from the slow cooker and onto a large plate. Pour the drippings from the slow cooker in a large bowl, and set aside for use in making the sauce. Use 2 forks to pull apart the pork. Discard excess fat.
Transfer the pulled pork back into the slow cooker, cover with the lid, and let it sit while making the chipotle sauce.
Add the chipotle sauce to the pulled pork, and mix together.
Serve on slider rolls while hot.
For the chipotle sauce
Just before serving, heat a medium-size pan on medium heat, and add the drippings from the slow cooker, water, tomato sauce, oregano, chipotle chili powder, vinegar and sugar. Stir.
Let cook until the mixture warms up (about 7 minutes).
To a small bowl, add the cornstarch and water. Stir until the mixture starts to thicken.
Slowly add the cornstarch mixture to the sauce, and continuously stir until the sauce thickens.