Both pork, though a beef roast would work in that green salsa too. The result should be like the shredded meats in a spicy sauce put into tortillas at Chilpolte. Chicken works too but cooked a shorter time.
The pork tenderloins are long thin pieces with almost no fat, but TJs has those in stock more often than a standard roast, go figure. I just cut the tenderloin in half to fit into the pot. It just falls apart when cooked. Most beef chuck roasts or pork roasts you cook whole, but can also make stews in crockpots.
Our TJ's has Kosher Stew beef i use to make Italian stew, basic stew with a can of TJ's diced tomatoes and seasonings. Tip...many standard crockpot recipes are already low carb by their nature of being just meat and veg.
Here is one paleo recipe site that lists the slow cooker recipes separately. Recently posted a beef burgundy and a butternut squash stew.
http://www.rubiesandradishes.com/ca...es/slow-cooker/