Place roast on a cutting board and rub the salt and pepper all over it; sprinkle the flour all over the seasoned meat and massage it into the flesh.
Heat the oil in a large sauté pan, set over high heat, until it is shimmering and about to smoke.
Place the roast in the pan and brown on all sides, 4 to 5 minutes a side, to create a crust.
Remove roast from pan and place in the bowl of a crock pot.
Add the butter and the pepperoncini to the meat.
Put the lid on the crock pot and set the machine to low.
As the roast heats, in a small bowl, combine the mayonnaise, vinegar, dill and paprika; whisk to emulsify; add the buttermilk if using, then whisk again.
Remove the lid from the crock pot and add the dressing.
Replace the cover and allow to continue cooking, undisturbed, for 6 to 8 hours, or until you can easily shred the meat
Using two forks, shred the meat without removing from the crock pot.
Mix the meat with the gravy in the crock pot.
Garnish with parsley, and serve with egg noodles, roasted potatoes, or pile on sandwich rolls, etc..