I don't have a meat thermometer! How can you tell if a pork loin is done? (in a crock pot)
The only way to be sure is to slice it through the center. Pork only needs to reach 144 degrees to kill its primary cause of food borne illness - the trichinosis worm. If the meat is slightly pink or white you are going to be way above that. Pork turns white at about 160 degrees.
I would let it rest for a few minutes before you slice it though, otherwise all of the juices are going to rush out through your cut.
140 is just about the right temperature, and yes it should rest but slow cookers kind of take care of that. As far as trichinosis I don't think there has been a case more recently than the 1930's.