Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
Hello and thank you for your question,There is one very common cause for the leak you are describing and it can be on one side of the truck and or leak on both side and its usually up front , the problem is caused poor sealing on the the roof ditch . I have enclosed the bulletin in the link below for your review as its very likely the source of your leak as well. Copy and paste the link below to your browser to open and view the fail.https://dl.dropboxusercontent.com/u/104923897/Water%20intrusion%20Nov%2023.pdf
The service bulletin may still apply, there is no way for water to inter the glove box with out coming from the front or top of the of the truck. Did you at least have a look at the roof body seal? After all water drips down hill.