I'm afraid I don't understand the UK side, and it affects some of the options you have later, so bear with me....
Unless you sell within 3 years of when you moved out, you will not satisfy the 2 out of 5 years exemption. To be precise, you have to have lived in the house as your principle residence for 710 days in the 5 years before the sale. I don't think you'll make it.
The fact that it's presently a rental makes the matter more difficult, as well. Basically, if you're a US resident, you need to be paying taxes on your world-wide income, include the rental income/loss.
But the gain (based on the US$ basis and and the US$ sales price) is taxed at a maximum of 15%. In addition, any depreciation on the structure that you claimed or should have claimed on the rental is recaptured at a maximum of 25%.
Finally, you can claim the Foreign Tax Credit for (approximately) the lesser of the UK tax due to the sale and the US tax due to the sale. It's probably best to use the "accrued" option on form 1116 so that the credit is properly aligned with the tax paid.
Alternatively, you can take the UK tax as an itemized deduction (under "taxes") on your 1040 Schedule A.
There should be a FX rate issue on the mortgage repayment, as well. I'd have to research how to compute that, and the nature of the gain/loss.