How can I thicken pulled pork (in a slow cooker)? Thanks!

Before trying a thickening agent, skim off excess liquid on top, or even put through a strainer and put back the amount of liquid you desire.
The pork should be the star, not the sauce. The sauce is just the decoration on the pork.
Hmmm, think I will do pulled pork later this week.

I would reduce it down separately and then add the cornstarch slurry for a little extra flavor.

Quickest way is a cornstarch slurry. Cornstarch with cold water (to prevent clumping) and toss in the hot pork liquid.

If you have a lot of liquid that cooked out of the meat, you may want to skim some off and reduce it separately. Some of the collagen that cooked out of the connective tissue will help as it cools a little, but not substantially thicken a sauce. With a slow cooker, I think the best bet is to remove some of the liquid and reduce it over a higher heat.