Fluid clarification
Starting in model year 2006, Dexron VI was introduced to meet the needs of the new 6 speed 6L80 and similar transmissions. It was backward compatible with automatic transmissions using Dexron versions of the past. It is NOT supposed to be used in anything else that originally used Dexron III, such as t/cases and manual transmissions. I believe that you can still use Dex III in non autotrac, i.e. manual or electric shift transfer cases, however, GM lists the following for your truck - Manual Transmission Fluid GM Part # 88861800.
Autotrac fluid has never been recommended for a manual or electric shift t/case found in HD trucks.
This bulletin spells it out. 04-07-30-037C Any vehicle that previously required DEXRON®-III for a manual transmission or transfer case should now use P/N 88861800. This fluid is labeled Manual Transmission and Transfer Case Fluid.
2004 LLY SC LB
ATS exhaust - BD LH Manifold
Kennedy Diesel Mega Filter & Lift Pump