Combine soda and 1/2 cup barbeque sauce in a multi-functional pressure cooker (such as Instant Pot). Add pork tenderloin. Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 50 minutes. Allow 10 to 15 minutes for pressure to build.

Release pressure using the natural-release method according to manufacturer's instructions, 10 to 40 minutes.

Remove pork loin and drain liquid from the pot. Shred pork using 2 forks. Return to the pot and mix in remaining 1 1/2 cups barbeque sauce.

Serve on hamburger buns and top with coleslaw.