Whisk the chili powder, cumin, paprika, 1 teaspoon salt, the cayenne and a few grinds of black pepper in a large bowl. Add the beef and toss to coat well. Set a 6-quart Instant Pot to sauté on high. When hot, add the vegetable oil, then add the beef in a single layer and cook, turning, until browned, about 10 minutes. Remove the beef to a large plate and cancel the sauté setting. Add 2/3 cup water to the pot. Use a wooden spoon to scrape up the bottom of the pot. Return the meat to the pot along with any juices from the plate. Put on and lock the lid, making sure the steam valve is in the sealing position. Set the pot to pressure-cook on high for 45 minutes. When the time is up, let the pressure release naturally for 15 minutes, then carefully turn the steam valve to the venting position to manually release any remaining pressure. Meanwhile, stir the ketchup, vinegar, molasses and brown sugar in a small bowl. Add salt, pepper and hot sauce to taste. Remove the beef to a clean plate. Set the pot to sauté on high. Add the ketchup mixture and simmer until reduced by half, 15 to 20 minutes. Meanwhile, shred the beef with two forks, discarding any large pieces of fat. Return to the pot and stir until well coated. Cancel the sauté setting and adjust the seasoning with salt, pepper and hot sauce. Divide the meat among the buns and top with coleslaw and pickles. Serve with chips.