One problem related to brake master cylinder has been reported for the 2006 Chevrolet Silverado. The most recently reported issues are listed below.
Saw wet spot under driver's side of truck, just behind engine compartment. Knew it wasn't good as the ac is on the other side. Figured I'd check it later. Started truck and as soon as I put my foot on the brake pedal, I could feel something was wrong. Stopped truck, popped hood and checked brake fluid level in master cylinder. Saw it was low. Added a pint of fluid and looked under the truck. Saw it leaking from a rusted out brake line near the abs module. All lines are rusted and in need of replacement.