I just tested our 35mm lens on an H4D system, and I was able to achieve an f stop of 3.5.
I have a few questions that may help narrow down what the problem might be.
Which Hasselblad body/ system are you using? Do you have the latest firmware updates on your body and lens? Have you been able to test your lens on a different body? Have you tried restoring the camera body to factory settings?