Hey Joel -- I'm surprised no one else has responded to you yet. I am no expert, so have hesitated to do so -- but here goes! I have some yellow leaves too -- I think they often go along with diseases. I have had good luck using a product called Bayer All in One. (There is a 2 in one variety -- I like the All in One.) It fertilizes and is a systemic insecticide and fungicide. When I faithfully apply that as directed, they are gorgeous all season long.
I wouldn't use it yet, since you just fertilized...

I would suggest calling a nursery that you trust and asking to speak with someone who really knows their roses. At the big Pikes out near us, there is an older fellow named Jack who is the unofficial rose man! You could maybe prune off a section that is yellow and take it in to show them.

Good luck!