Have a 2008 Chevrolet 2500 diesel with 120,000.miles. This has excellent maintenance. Most people think it is new. We have just started getting a smell of crayons. Only happens every once in a while...
The DPF could be on regen and developing more than the 1,200 degrees it created when new. Could be burning paint or bed-liner. Maybe a leak has caused fluid to migrate to the DPF.