High Output Alternator for GMC Sierra (2008-2009) 6.6L

Heavy-Duty 350-Amp High Output Alternator for 2008-2009 GMC Sierra (GMT900)

What it Does: The 350-Amp High Output Alternator replaces the factory low-amperage charging unit on the 2008-2009 GMC Sierra 6.6L to deliver reliable current capacity for extreme auxiliary electrical loads and eliminate system voltage drops.

The Stock GMC Sierra Electrical Bottleneck

Factory charging systems on the GMT900 platform equipped with the 6.6L Duramax LMM were engineered with alternators rated at only 125 to 145 amps. When running dual battery banks, high-draw winches, commercial snowplows, high-wattage inverters, or auxiliary lighting, the factory unit suffers from severe thermal saturation. At idle speeds, OEM rectifiers overheat, causing system voltage to sag below 12.8 volts. This induces chronic undercharging, early battery bank degradation, and sensitive ECM sensor erraticism under continuous commercial loads.

The Engineering Solution

Manufactured in the USA, this 350-amp alternator delivers superior charging stability using heavy-duty copper stator windings, dual internal cooling fans, and high-amperage avalanche diode rectifiers designed to withstand extreme underhood thermal environments. Engineered for bolt-in compatibility with factory accessory brackets, it resolves the load demands of the 6.6L Duramax LMM without requiring pulley spacers or modifications. It replaces factory assemblies directly, including OEM reference numbers 8301, 8301N, 15093928, 15857608, 15095871, 25877026, and 8301-350A.

What's Included

• 1x 350-Amp High Output Alternator

Technical Specifications

Compatibility

• 2008 GMC Sierra 2500HD 6.6L V8 Duramax Diesel (LMM)
• 2009 GMC Sierra 2500HD 6.6L V8 Duramax Diesel (LMM)
• 2008 GMC Sierra 3500HD 6.6L V8 Duramax Diesel (LMM)
• 2009 GMC Sierra 3500HD 6.6L V8 Duramax Diesel (LMM)

Frequently Asked Questions & Fitment Warnings

Does this fit the GMT900 Sierra?

Yes, this is a direct fit for the 2008-2009 GMC Sierra equipped with the 6.6L Duramax LMM turbo-diesel engine.

Do I need to upgrade my main charging cables?

Yes, a heavy-duty 1/0 AWG "Big 3" wiring upgrade is strongly advised to support this unit's 350-amp flow without introducing circuit resistance or heat hazards.

The GMC Towing Caliber

Heavy-duty trucks built for severe towing, snow removal, and job-site performance require electrical systems that match their torque. This high-output unit ensures steady 14-volt reserve power under the harshest work conditions.