Running a marathon - foot discomfort and advice?

I've been training for a marathon that is two weeks from now. I've run 35-40 miles/week for several years now (pain free), and I ran 21 miles (3h05m) last weekend without any muscle pain, and I didn't hit "the wall". However, my right heel is sore (much more so today than it was yesterday or the day before). I'm wondering how best to handle this and what I should do in the last few weeks to prepare myself...the marathon is in Austin, which has a reputation for being "hilly".