I've had a similar problem with both Avalanches I've owned, a 2003 and currently a 2005 LT. I haul equipment every weekend that CANNOT get wet. I think the Avalanche is the PERFECT truck, but sadly I'm thinking of having to switch to a regular SUV because of the hassle of having to unload equipment every time it rains, instead of leaving it for the morning (I'm a musician, so it's often late when I get home!) Here is the problem: regular light rain, no problem. Heavy rain, and it leaks in certain spots between every bed cover! The worst is the seal between cover #1 and the rear window. Sometimes you just want to slap those engineers...they make this awesome utility vehicle, but they screw up the cover system. Did you ever notice that the three covers are slightly curved to the outside? This I believe is intentional and makes sense in order to channel the water to the outside gutter system. HOWEVER, have you also noticed that the curvature REVERSES when it gets cold out - say, anything below about 50 degrees without the sun shining? Then the water stays in the middle! it has nowhere to go but build up and leak somewhere! Warm day, sun shining, no problem...the covers are curved towards the outside. Cold weather days, they change. Frustrating! What idiot engineers didn't anticipate this??
Is there ANYONE who knows a fix?