I use FP-3000B outdoors in sun all the time. I can't scan 100B negatives and it is a pain in the a** to 'inventory' both film types. If you do the math you'll see that diffraction is NOT your problem. The film size, print size, and print resolution do not allow diffraction to have any measurable effect.
I would not shoot Delta 3200 on a sunny day, because it will not hold up to enlargement. At 24mm x 35mm, that negative looks nice and sharp to your eye.
Your problem is more likely that the large amount of light is amplifying light leaks and increasing glare in the lens elements. If you look here, you'll see a photo taken in full sun with FP-3000B: http://www.flickr.com/photos/amuderi...ream/lightbox/
My advice is just to try another camera. There are so many out there. It almost isn't worth really trying to 'fix' one when you will eventually find one without problems.