Rub the salt and garlic powder into the beef roast. Pour broth into Instant Pot and place the chuck roast in the bottom of the pot. 

Cover and lock the lid into place. Make sure valve is set to sealing. Set to cook on manual/pressure for 70 minutes. When time is do a quick pressure release. 

Open the Instant Pot and place a steamer basket on top of the beef. Add the potatoes to the steamer basket. If you don’t have a steamer basket just add the potatoes straight into the Instant Pot. Lock the lid into placeand make sure valve is set to seal. Cook on manual/pressure for 8 minutes. When the time is allow the pressure release naturally for 15 minutes then move to quick release to release any remaining pressure. Remove the lid.

 Add the potatoes into a large bowl and mash. Add in the butter, milk, kosher salt, garlic powder and sour cream and stir/mash until smooth and creamy. 

Move the roast to a cutting board and let it rest. Turn the Instant Pot to the saute setting. Slowly whisk in the water followed by the gravy packages. It will start to thicken in a couple of minutes. To make a thicker gravy add in a cornstarch slurry (in a small bowl stir together 1-2 Tbsp of cornstarch with 1-2 Tbsp of water, until smooth.Then pour the mixture into the Instant Pot. The cornstarch mixture will thicken up contents of pot quickly). Add salt and pepper the gravy to taste.

Slice the roast or shred it. Toast the slices of bread if desired. Place 2 slices of bread on a plate and top with a portion of roast beef on. Scoop some mashed potatoes on the plate. Ladle gravy over the top of the sandwich and mashed potatoes. Serves 6.