[Diesel_Dave]

My truck (2007.5) was the first one with a VG turbo and has closed-loop AFR control. That being said, there's still an benefit, because if the air can get to the compressor better, then the VG won't have to close down as far to deliver the same air. Therefore, exhaust manifold pressure goes down and, therefore, pumping loses go down--you pushing against less pressure during the exhaust stroke. It all sounds complicated, but I've seen it proven with an engine in a test cell.

If the diesel doesn't have a VG turbo, then you correct--the benefit comes from higher AFR.