Merchant 121002A Allison 5 Speed Overhaul Kit W Pistons | 2001-2005 GM Silverado/Sierra 2500HD/3500HD 6.6L Duramax

Features:

• Fits 2001–2005 Silverado/Sierra 2500HD and 3500HD
• Compatible with 6.6L LB7 and LLY Duramax engines
• Includes all paper and rubber components
• Contains metal clad seals and sealing rings
• Comes with bonded pistons for durability
• Ideal for basic transmission reseal and refresh
• High-quality gaskets ensure long-lasting repairs
• Sealing components built to OEM specifications
• Pan gasket included for a complete reseal
• Does not include filters or clutches
• Great for preventative maintenance or rebuilds
• Designed specifically for Allison 5-Speed transmissions

Bring Your Allison 5 Speed Back to Life

If your Duramax’s Allison 5-speed transmission is starting to feel a little tired, this Merchant Automotive Overhaul Kit with Pistons is exactly what you need to breathe new life into it. Packed with all the essential seals, gaskets, and bonded pistons, it’s built for guys who want to reseal and refresh their transmission the right way without chasing down a bunch of separate parts. Whether you're chasing leaks, shifting issues, or just getting ahead of future problems, this kit gives you the confidence to tear in and get it done right the first time. Everything inside is high-quality and made to meet or exceed OEM standards, so you know it’ll last under real-world use, not just in theory. Designed for 2001–2005 Silverado and Sierra 2500HD/3500HD trucks with the 6.6L LB7 or LLY Duramax, this overhaul kit has been trusted by pros and DIYers alike for years. It's a smart investment if you want to get the most out of your build without the stress of mystery leaks or worn-out seals. Your truck works hard — your transmission should too.

Precision Components for a Reliable Transmission Reseal

The Merchant Automotive 121002A Overhaul Kit is engineered specifically for 2001–2005 GM Silverado and Sierra HD models equipped with the 6.6L LB7 or LLY Duramax engines paired to the Allison 5-speed automatic transmission. This kit includes all critical paper, rubber, and metal-clad seals, along with the bonded pistons necessary to properly reseal and refresh the transmission internals. Each component is built to exacting specifications to ensure consistent fit, pressure retention, and long-term durability, even in demanding towing or heavy-use environments. The CNC-formed sealing rings and reinforced pan gasket ensure that leak points are properly addressed during reassembly. It's important to note that this overhaul kit focuses on sealing and piston components only — filters, clutches, and other hard parts must be sourced separately if needed. By targeting the most failure-prone areas, this kit provides a reliable foundation for any rebuild or refresh project. Whether you're addressing early signs of wear or doing preventative maintenance, this Merchant Automotive kit offers the precision and quality your Allison transmission demands.

Fits: 2001, 2002, 2003, 2004, 2005 GM 2500HD/3500HD 6.6L Duramax

Notes:

• Kit is designed for 2001–2005 GM 2500HD/3500HD models
• Fits trucks equipped with 6.6L LB7 and LLY Duramax engines
• Intended for Allison 1000 5-speed automatic transmissions
• Includes seals, gaskets, sealing rings, and bonded pistons
• Filters, clutches, and hard parts are not included
• Ideal for basic reseal or preventative maintenance jobs
• Components meet or exceed OEM quality standards
• Professional installation or advanced DIY skill recommended
• Pan gasket included to complete reseal process
• Great solution for addressing common transmission leaks
• Always inspect clutches and hard parts separately before rebuild
• California residents must review Prop 65 warnings