Slow cooker cooked too fast

Keep the lid on and make sure there is liquid in the pot so it doesn't dry out. The idea of slow cooking isn't that food will only reach temperature at the end of the allocated time, it is that the extended time changes the texture of the meat and allows flavours to develop and blend further.

Pork loin is very lean and tender, so it's a bad cut for a slow cooker. Slow cookers work best with fatty or collagen-rich cuts that should be held at a high temperature for long enough for the connective tissue to "melt" and create a super rich, tender result. Pork loin will simply dry out. I would remove it from the cooker and chill until dinner. Either reheat gently or serve cold tonight. In the future, be wary of recipes that involve lean, tender cuts in a slow cooker.