Add the mayonnaise, sugar, lemon juice, white vinegar, salt and pepper to a large mixing bowl and whisk together until fully combined.
Add in the coleslaw mix green cabbage and carrots and stir well to combine.
Make Pork Tenderloin:
Place pork tenderloin and water into slow cooker and sprinkle with garlic salt and pepper if desired. Place the lid on top and set heat to low for about 8 hours or until internal temp is 145°F (medium rare) and 160°F (medium). Drain liquid from slow cooker then shred meat using two forks. Toss with barbecue sauce.
Remove cranberry sauce from container.
Butter top of bun and lightly toast, if desired. To assemble, place shredded pork on top of the bottom bun. Top with a good spoon worth of cranberry sauce then coleslaw and top with the bun.