Burning oil?

[01excursion7.3]

My buddy followed me for a lil while tonight, and said while he was following me, that my truck smelt like it was burning oil, like older rigs would smell. Any idea if this indicates an issue, or is he just smelling the diesel burning? Now mind you, he was also driving a PSD, and said he only smelled it while behind me.

I did drive it kinda hard for a while today, but I was done horsin around well before this.