What month in 2004 did the truck go 'In Service'? GM has an 8 year/80,000 mile warranty for the catalytic converter but "the applicable warranty period shall begin on the date the vehicle is delivered to the first retail purchaser..."
So you may be able to, based upon mileage and in-service date, get it replaced under warranty.
http://www.justanswer.com/uploads/mc...l-Warranty.pdf