2002 GMC C3500 front rotors

You may have some bad calipers, the way to check them is;
1. Jack up the front of the van, until the tires are off the ground;
2. Turn the tires by hand, there should be no resistance, apply the brakes, spin the tires again, make sure there is no resistance.
But I think the real problem is, you have that Van very loaded, and you are waiting for the last second to slam on the brakes, try cruising a little more, in other words, when you see the light red ahead of you, take your foot off the accelerator, and try to cost, and try applying your brakes gently, 200 yards before you need to stop.