Place your roast in Instant Pot and pour salsa and soda over the roast. Sprinkle the brown sugar on top.
Place the lid on top of the Instant Pot and move the valve to SEALING. Press the MANUAL (PRESSURE COOK) button and set timer for 60 minutes (or 20 minutes per pound, depending on the size of your roast).
When the timer is done, let the pressure do a NATURAL RELEASE and let it sit in the Instant Pot on the keep warm setting for at least 1 hour (I even prefer to let the roast sit in there for a couple hours to make sure it is super tender).
Remove the lid and shred the roast with 2 forks.
Drain liquid and shred pork. Save some liquid and mix it back in with the pork to keep it moist.
Preheat oven to 350 degrees F.
Evenly divide pork, refried beans and cheese between 8 tortillas.
Fold up each tortilla into a rectangular packet around the filling and place folded side down in a 9 x 13 inch baking dish.
Spray the tops of the chimichangas generously with nonstick cooking spray (you could also use a pastry brush and lightly brush the tops with olive oil).
Place in preheated oven and bake for 15 minutes.
Remove from oven, turn over each chimichanga and return to the oven to cook for an additional 15 minutes.