In a small bowl combine the brown sugar, salt, pepper, garlic powder, and chili powder. Stir to combine. Rub on pork.
In the base of an instant pot or pressure cooker, combine the seasoned pork tenderloin, apple cider vinegar, and stock. Secure the lid onto the pressure cooker. Turn on instant pot, select "Pressure Cook" setting, set to "high pressure" for 18-20 minutes*, and start.
Once the timer has expired and the pork has finished cooking, allow the pressure to release naturally. The pork should temp at 155 degrees F. once done. Remove from instant pot and allow to rest.
While pork rests, whisk flour into the remaining drippings while still warm. If the gravy is too thick, thin with a little stock. Adjust seasoning as needed.
Serve pork sliced with gravy. Leftovers will keep in an airtight container in the fridge for 3-4 days.