You're kidding about your GPA, right?
If you're going to care about the difference between a 3.7 and a 3.9, then I wonder how long it will be before you start driving yourself nuts in a program. Nobody expects perfectionism, but everyone is a perfectionist. You just need to learn to manage that and right now you can be saying that there is no real difference between a 3.7 and a 3.9, but it is a big difference between a 2.7 and a 3.7, right?
If you're very serious about American history, don't do the UK. Do the UK, if only you're planning to include some British into your work. Otherwise, you'll be stranded when all of your sources are 6,000 miles away. Although doing a one-year MA in the UK is okay because you're getting it in less time than doing a US one. However, you most likely won't even be ready to apply for the PhD when you start that program because you don't have much to show. So if you're looking to do one-year MA program in the UK, plan on waiting another year to apply (and figure out something to do in the meantime!)
Try to get a mix of public and private schools for the PhD. Many, many programs are having problems with finances and the public ones are most vulnerable because anything can happen with the states' budgets.
Anyway, I second StrangeLight's thoughts. Just adding my own here.