Chevy welds the roof panel to the car but instead of doing the body work to finish the area smooth, they cover it with a piece of molding.  This molding is held on with double stick foam tape.  Auto manufacturers use a lot of this type of tape to fasten trim to cars.  The molding itself is a soft vinyl-type of plastic molded around a stainless steel core.  Unfortunately, the trim is not bent to the shape of the roof so when it is applied to the vehicle, the ends want to spring back.  This constant tension causes the tape to slowly release from the car.  This deforms the windshield weatherstrip and looks unsightly.

Does your car look like this?  This is the roof molding on the top of the windshield on the driver's side of my car.  Strangely enough, both the front and back of the driver's side is lifting, but not the passenger's side.
To do this repair, I got the same 3M molding tape that the manufacturers use.  I also had a bottle of un-du.  If you have never heard of this product, it un-sticks any self sticking adhesive (tape, decals, labels, automotive molding double stick tape...)  The really neat thing is that after the liquid dries, the adhesive regains it's sticky properties.  Un-du doesn't harm most surfaces and leaves no residue.  I got this large 4 oz bottle at Wal-Mart for $4.
The bottle comes with a neat applicator/scraper that directs the liquid to the area you want to work on.  I lifted the edge of the molding with the scraper and let the liquid drip down.  I used the applicator to apply gentle tension to lift the molding up.  Let the un-do do its job and the trim will come up.  As one area pops up, move the bottle further back and repeat the process.
After a while, enough molding will come up so you will be able to work with it.  WARNING!!! Do not bend the molding up.  The steel core will bend and you will have a VERY difficult time straightening it.  
I twisted the molding so you can see the tape.  Don't do this too much or you won't be able to straighten it back.  You can use un-do to clean off the tape and stick it back to the car.  I chose to replace the tape with a new piece.
The tape is pretty soft so you can rub it and it will shred.  After I got to this point I used more un-do to take off the residue.  I took off about 3 inches.  The rest of the tape looked OK.
Here is the tape.  Cut off the length you need and stick it to the trim.  Make sure you clean off channel where the tape will be applied.  Funny thing is, there seems to be another type of foam tape on the roof that you stick the molding tape to. So it's like a sandwich, roof, foam tape, molding tape, trim.
Remove the red protective film and press the trim into place.  A trick to get the protective film off is to stick a small piece of duct tape (masking tape is OK too) on a corner of the film.  When you are ready to remove the film, pull use the duct tape as a tab and peel the film right off.

The windshield weatherstrip looks like it is still lifted.  I am hoping that it will settle back into place now that it isn't being forced up by the molding.  I'll see if this repair holds before I work on the rear part of this molding.

After a few days, it looks like this fix might not hold up.  Now the existing black foam tape is seperating.  The next step will be to try some silicone adhesive.  I'll let you all know how this works out.

I found out that Chevy had a TSB addressing this problem so I took the car in and had them fix it.  On a side note, if you are out of warranty or want to do this yourself, Eddie told me not to use a silicone adhesive.  It will cause metal corrosion on bare metal and will prevent other adhesives from sticking.  This would be a problem if you ever needed to replace your windshield and the silicone contaiminated the contact surfaces.  HE recommended Essex u-418 HV.