What temperature should a pork loin be when cooked in a slow cooker or how long should it cook?
Loin or tenderloin is a very lean cut of meat and should not be cooked in a slow cooker.
Slow cookers are better suited to cuts of meat with high amounts of connective tissue, like pork shoulder or chuck roast, that turns into gelatin as it cooks for a long time.
IMHO, tenderloin should be grilled or broiled just until the center is 145° or so. Then rested and sliced.
Totally agree with above answer. However I have done both pork loin and tenderloin in a slow cook/braise method and the meat will be dry but this can be made delicious by making sure to thicken your braising liquid at the end then applying it back to the meat. Just be sure to not add much salt to braising liquid until after reduction.