Yes the trim must be inserted in the gasket slot, then installed on the windshield before the assembly can be mounted on the truck. To remove the trim, the glass must be removed from the truck before the trim can be removed from the gasket.
The lowest risk to the glass and the trim is to cut the gasket free from the truck with a utility knife all around the perimeter. It's easier to reach the gasket from the outside, but if the gasket has turned to wood, it may be easier to cut through the rubber lip from inside the cab and then push the glass forward.
Trying to remove the trim from the gasket while still mounted on the truck, will almost always result in damage to the trim.
Last edited by Markeb; 10/24/2009 8:23 AM. Reason: another thought