Always check the temperature in several spots to be sure you hit the right spot(s). If the thermometer showed 155 and it was red in the center, either the thermometer is defective or it was stuck into the wrong part of the meat.
Check the thermometer in boiling water and iced water to ensure the temps are accurate. Look for 212 F and 32 F.
Try to put the probe into the meat so the end is in the very center of the thickest part of the meat.
Pork is safe to eat at 137 F.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan