Place the roast in the slow cooker and pour the ketchup, brown sugar, onion, and Chipotle sauce over top.
Cook for 4-6 hours on high, or 8-10 on low.
Remove meat from slow cooker, and shred.
Return to the slow cooker, stir, and cook on low until ready to serve on buns.
Notes
I love the Old El Paso brand chipotle sauce that comes in a little pouch (just a personal opinion!!!)
To turn this into a freezer meal:
Add roast, ketchup, brown sugar, onion, and chipotle sauce to a gallon-sized freezer bag. Squeeze out as much air as possible and seal bag closed. Place freezer bag into freezer and it will last 60-90 days. When ready to use, spray inside of slow cooker with non-stick cooking spray and dump ingredients from bag into slow cooker. Place the lid on top and cook for 8-10 hours on low heat (you can cook it for 5-6 hours on high heat, but it will not be as tender as cooking it low and slow).