I was an auto glass installer for 24 years some things to think about this should be a very easy install but sometimes they are a real pain in the but is the gasket made right is it real stiff is it real cold how was it packed that can be a real big deal. not all glass is the same size or shape even if it is the same part number or even made by the same company. the window opening of your truck do you think they are all the same size they are not I have roped in some windows that were so loose they rattled and felt like they could fall out and others that were so tight that a hard bump in the road might stress crack them.fitting the glass to the truck before hand and knowing what to look for makes all the difference some times I will use a wet belt sander to the edge of the glass if needed but if the glass is very old fragile the pinch weld might need some grinding. warming the rubber with a heat gun might help. in all my 24 years I have never used a rubber mallet use your whole hand palm and fingers hitting at the same time to disperse the inpact to the largest earea less chance that way of brakeage . sorry about the bad spelling . neil