So I've been playing PoE a bunch the past couple of days, but steam is still not showing me as having the Kickstarter backer achievement. The DLC section shows me as having the backer achievement and item, but it's not actually triggering.

Is there a fix for this? I have tried closing and restarting steam.

This worked for me: once the game is attached to your Steam profile (i.e. you can see click the link to see your achievements), just start a new game.  When you get to the caravan campsite after character creation, it should pop.

That did the trick, thanks!