rust bucket
 

My new 2013 gmc sierra truck ,has 2600 km .

Take it in! That's covered under the bumper to bumper and corrosion warranty. That will absolutely be a covered repair. Totally sucks though ...

WOW !!! I would be pissed too. Absolutely !!! Take it in. Be nice about it until they start to give you the run around then demand results

i would check to see if your window and door seals leak my former boss had this issue but a little worse he actually had water collecting in the bottom of his apperantly the seals were lose or not installed properly but yes take it in and i would also be pissed