I have an '08 Dodge with the 6.7 and a manual tranny. I don't know when they started using the double disc clutches but they're famous for failing. Mine started slipping at about 90k. I had it replaced with one that they said should last the life of the pickup. If you can do it yourself, they're not real expensive but I don't have the means to DIY.

“In a time of deceit telling the truth is a revolutionary act.”
― George Orwell

It's not over when you lose. It's over when you quit.