Issues with 8.1 Vortex with Allison Transmission

Transfer case has an engineering defect where an internal ring will vibrate against the housing eventually causing a small pin hole in the housing. For more than you'd want to know on this see this:

Pump Rub


Also brake/transmission/oil cooler lines rusting out is a known issue too. But that's not confined to the Chevy/GMC 8.1 trucks but rather many from 2000-2009.