Yes, GM issued a TSB which called for replacing the rectangular magnets with new, circular magnets.
http://www.rockauto.com/en/catalog/chevrolet,2007,tahoe,5.3l+v8,1433255,transmission-automatic,oil+pan+magnet,18538
There's the link to the new magnet they are recommending now. I don't know if you have the 4.8L or 5.3L, but the magnet is the same.
I also second the Magnefine inline filter.