[xlr8or]

I would check the windshield frame for flex and that is mounts solid without stressing the brackets. If it is mounted under stress it will transfer that to the glass. Are you replacing the glass with the frame out of the car? I would have the frame in and then mount the glass. If the glass is mounted first then you may be putting stress on the frame that eventually pops the glass.
Solid windows should never be mounted under stress. They should fit cleanly and have any gaps filled from behind to have a consistant surface to mount to.
If you ever watch a windshield replacement on a new car, they cut out the old window and then lay a thick bead of a heavy rubber material that cures after the glass has been set into it and basically holds it in like glue so there is zero stress on the glass.

Hope this helps.

Scott