For Christmas (2012) I got the Slow Cooker Revolution cookbook. Years ago, my slow cooker philosophy was to throw it in, turn it on, and 10 hours later it should be perfect. And mostly this is true -- but everything tasted the same and had the same texture (mush). So THIS recipe isn't straight up slow-cooker, but the meat came out fork-tender and incredibly tasty.
Heat oil in 12" skillet over medium-high heat until oil shimmers. Add onions, garlic, tomato paste, and thyme and cook until onions are softened and lightly browned, 8 - 10 minutes. Stir in flour and cook for 1 minute. Slowly whisk in wine, scraping up any browned bits and smoothing out any lumps; transfer to slow cooker.
Stir tomatoes, carrots, and potatoes into slow cooker. Season roasts with salt and pepper and nestle into slow cooker. Cover and cook until pork is tender, 9 - 11 hours on low or 5 - 7 hours on high.
Transfer roasts to cutting board, tent loosely with aluminum foil, and let rest for 20 minutes. Let braising liquid settle for 5 minutes, then remove fat from surface using large spoon. Stir in vinegar and season with salt and pepper to taste.
Remove twine from roasts, slice into 1/2" thick slices, and arrange on serving platter. Spoon 1 cup sauce over meat and serve with remaining sauce.