How to Remove Headlight Housing?

I haven't been able to remove either headlamp housing on our '08 Uplander, which is necessary to replace any of the front lamps. How is this supposed to be done? I have followed the manual's instructions of removing the pin and screw, but it won't budge. The local Chevy dealer told me to pull harder, but also to be "very careful"....which doesn't make sense. If I were to pull straight forward, I think that would tear and damage the rubber gasket that runs around the headlamp housing perimeter.