Just an FYI, I just applied today for a GRADPlus loan.
I initially started out on my schools website for GRADplus loans...I went through the whole process, picked a lender from their list (the one with the best rates) and was DENIED. I was really upset about this because I have average credit, with absolutely no delinquences over 90 days ever and none those things that would cause me to be denied. The only reason my credit score isn't higher is because I have a fairly high revolving credit balance. They said they would send me a letter in the mail stating their reason for denial.
So I decided to try another lender, seperate from the online portal from my school and went to the student loan discount page on finaid.com, and slected one of the lenders with better terms, AFC Student loans http://www.academicfinancing.com/
and filled out there application. It turns out that this is same firm that holds my loans for UG and I was preapproved!
So if you don't have any luck witht he first place you try, try another. Its very strange, because I was under the impression that GradPlus loans didn't really take many credit factors in account.