[grumpyolddog]

I would still be looking at the antenna on the roof or the windshield. I work at a gm store in the bodyshop and have seen leaks in both areas. Where was your truck built? The ones built in Mexico have been the ones that leak around the windshield sealant. If you use soapy water on the outside of the windshield edges and blow compressed air around the inside of the roof and a pillar it will bubble on the outside where the leak is. If the roof antenna is leaking look under the a pillar trim for water trails and stains on the corner of the headliner at the top of the a pillar.