wipers out of sync
 

At first the left one didn't go all the way across to the left, though the right one did. I adjusted the left one to match the right, but now it moves much more slowly than the right one, and they collide. Anyone have any ideas on what might be going on?

put up your hood and watch the mechanisms... see if you can spot an abnormality.

Are you sure you fully tightened the nut at the base of the wiper arm? If it is loose, the arm movement will lag.

Ah. There's a nut.... I didn't spot that. That sounds like the problem. I'll go look more closely. Thanks Boxtaboy!

Yep, if you look at the base of the wiper arm, you can pluck off the plastic cap that covers it. Then, you'll see a nut there. Tighten it, and you should be good to go.