Time: Over night (12 - 20 Hours)
Trim the fat off of the roast and place the roast into your lined slow cooker. (I use Reynolds Wrap Slow Cooker Liners. Make sure the size fits your cooker) Sprinkle the Italian Salad Dressing Mix over the roast and then pour the entire jar of peperoncini over the roast, juice and all. (Don't worry it does not make it super spicy. My mom was really worried about that!) Put the lid on your slow cooker and turn the dial to Low heat.
About an hour before you want to eat dinner take a spoon and scoop out all of the peppers and throw them away. (I save the jar and put them back in and toss the jar) Grab a bowl and scoop out the chunk or chunks of beef. Shred the beef in the bowl a little at a time so that you can pull any excess fat out. When all beef is shredded drop it all back into the cooker. Add the package of Au Jus Mix and combine well with the shredded beef. Let the beef cook for another 30 min to an hour on Low.
In a pan heated on medium high heat melt a tab of butter or a little olive oil. Open each hoagie and lay them flat on the pan. I can usually get two in the pan at a time. Let them sit in the pan open face down for 1-2 min or until they are golden brown. If you do a second batch add a little more butter or olive oil. Use a fork or tongs to dress each hoagie roll with a serving of beef. Add cheese or other toppings if you would like but it is amazing on it's own! Use a ladle to scoop out a serving of Au Jus for each person for dipping. (Clear plastic party cups work well for this or if you have the cute little personal dipping bowls that will work too!)
Cook on low heat over night and all day the next day. I put it in the cooker right before we go to bed and then forget about it until the next afternoon. It is fine to slow cook for 12 - 20 hours. Putting it in, in the morning and having it for dinner that night is just not gonna happen. I have tried it and it doesn't work. (Even with High Heat) You want the beef to be super tender so you hardly touch it and it shreds. Don't lift the lid until you are ready to shred the beef. You want all of the heat to stay inside the cooker all night and day.