Ok, I have had this problem for about a year. Thought I had it fixed, but I noticed it again the other day. I was vacuuming my truck and noticed some dampness under the carpet. I thought it may have been from the condensation tube, but I have unclogged that. Yesterday we had a lot of rain, and my passenger side was soaked, pulled up the carpet and there was a huge puddle. I think there is a leak somewhere. What could this be?

 

What year is your truck? Where did you see the dampness, front or back? I had a '99 GMC that went through 4 back windows before it finally sealed properly. If it leaks that bad, you should be able to get inside and let someone spray it down really good with a nozzle and you should be able to see the leak. If you think it might be the back window, it is probably happening in the seams of the outer seal.

 

I have a 2001 regular cab, it's not coming from the back. somewhere in the front, not sure if it is from the firewall, or the door seals.

 

In that case, I would say door seals. Should be easy to find.

 

Just for ***** and giggles, I would check the heater core too.

 

Yeah, I have had people tell me that. But, doesn't the heater core leak coolant? 'cause I am leaking water.