Preheat oven to 275 ℉.
Heat olive oil in a large Dutch oven pot over medium heat.
Add beef roast and sear on all sides until golden brown, about 8-10 minutes.
Remove browned roast from the pot and set aside.
Add butter to the pot and cook mushrooms unit they releaser their liquid and they are golden brown, about 5-8 minutes.
Return roast along with any juices on the plate back to the Dutch oven pot with the cooked mushrooms.
In a mixing bowl combine; French onion soup, pepperoncini peppers and their juices, au jus seasoning mix and reach seasoning. Stir to combine.
Add the sauce to the Dutch oven pot with the roast and the mushrooms.
Cover pot with a tight fitting lid and place it in the oven.
Cook for 3½ to 4 hours or until beef shreds easily with tongs.
Cut hoagie rolls in half and place sliced cheese onto rolls.
Place rolls in the oven and set oven temperature to "Broil". Toast until cheese is melted, bubbly and begins to brown slightly.
Remove rolls from oven and top with a heaping mound of the shredded beef.
Serve each sandwich with a side of the sauce for dipping.