how big is your kettle? Sounds like it is about an 8 gallon kettle?

Let's assume that you went to boil with 8 gallons and ended up with 7 gallons after 60 minutes. This means that you boiled off about 12.5% in one hour.

Next time, if you want to end up with 5.5 gallons after 1 hour, you should shoot for about 6.2 gallons pre boil (5.5 x .125 + 5.5). There are calculators online to help you with your mash and sparge calculations such as:

http://www.brew365.com/mash_sparge_water_calculator.php
Keep in mind for higher gravity beers, you must mash and sparge with more water to get the efficiency that you're after. To accomidate the extra water, you will need to boil longer - like 90 minutes or so.

My method is to follow the calculator, with 15 minutes left in my boil, I put my measuring stick into my wort to see how many gallons I have. Then I adjust my btu's to either more or less aggressively boil so that I end up w/ the correct amount of wort.