Outdoor Lighting Question

I was outdoor taking photos and noticed that a bunch of my photos seemed to be really overexposed. It was cloudy outside, so no sunlight. I was using a 24-85 f/2.8-4 on my D90. I also have a SB600.

Is this a problem with my metering, or do I need a faster shutter speed? Just wondering what I'd need to do to not have it so overexposed.

Thanks for any help/suggestions.