Rinse the pork loin in cool water and pat completely dry with paper towels.
Trim any silver skin and excess fat from the loin, leaving at least a 1/4″ of fat cap on for moisture and flavor.
Place the pork loin on a sheet pan.
In a mixing bowl, whisk together the salt, sugar, pepper, celery seeds, garlic powder, onion powder, cayenne, and five spice powder.
Coat the entire loin with olive oil.
Rub the meat all over with the spice mixture.
Set the loin aside and allow it to come to room temperature for approximately 40 minutes.
Fill the hopper of the Traeger grill with enough wood pellets to last up to 3 hours.
Turn the smoker on with the top open until a flame is visible, approximately 5 minutes.
Close the top of the grill and set the temperature to 225˚F.
Preheat the grill for approximately 10 to 15 minutes.
Place the seasoned pork loin, fat side facing up, on the grill rack inside the smoker.
Insert the probe thermometer into the thickest end of the pork.
Close the top and set a timer for 2 hours.
Check the temperature of the meat at 2 hours.
You are looking for an internal temperature of 145˚F.
Continue smoking until the desired temperature is achieved, checking every 15 to 30 minutes.
When the pork is at the desired temperature, remove it to a clean cutting board and cover it loosely with aluminum foil.
Allow the meat to rest for at least 20 minutes before slicing.
Slice the loin thinly and place on a platter for serving.
Serve with a side of sauce