If you sell property and have a one-time gain on your taxes that is disproportionate to your annual income, is that one of the reasons that you can use the “alternative documentation” approach to having your IBR payment calculated?  What do they require for alternative documentation?  A statement from your employer as to your salary?

Did some research online and found that you “may” use the Alternative Documentation of Income form (http://www.loanconsolidation.ed.gov/forms/adoi.pdf) if your AGI does not reasonably reflect your income.  So that would appear to be the case for a one-time gain.