Allison Stage 1 500 HP 2001 - 2019 (WHOLESALE)

The Allison Stage 1 from Next Level Engine & Transmission is designed for 2001–2019 Duramax-equipped trucks producing up to 500 horsepower. This transmission delivers the strength and dependability your truck needs for towing, daily driving, and mild tuning — all while maintaining the smooth, consistent shifting the Allison name is known for.

Each transmission is assembled by a master technician using premium components and proven assembly practices to ensure lasting reliability and performance. Once complete, the technician personally signs the transmission — a mark of craftsmanship and pride that represents the Next Level standard.

The Allison Stage 1 offers a balanced upgrade for stock and lightly modified trucks, improving shift quality, cooling, and overall durability without compromising drivability.

Recommended For

• 2001–2019 Duramax trucks
  
• Stock to mildly tuned builds up to 500 HP
  
• Towing and daily driving applications
  
• Drivers who want reliable performance with enhanced durability

This Transmission Features The Following:

Tear Down & Cleaning:

• The transmission is fully disassembled, and all soft, wear-prone parts are replaced with brand-new, high-quality components.
  
• Cases and housings are deep-cleaned in a 190° hot wash system to remove all residue and contaminants.
  
• Hard parts are hand-inspected and cleaned individually, with any questionable components replaced before reassembly.
  
• The case is thoroughly checked for cracks, wear, or damage to ensure a flawless foundation for the build.
  

Upgraded Internal Components:

• Raybestos or ALTO G3 C-3 and C-4 packs with additional clutch count
• Billet Torque Converter
• Modified lock up valve
• Modified Trim Valves
• New bonded pistons
• New OEM Bearings
• HD C1,C2,C3,C4 and C5 Clutches
• Next Level Custom Paint

Warranty:

Includes: a 2-year / unlimited miles warranty. 

Note:

Next Level Engine & Transmission reserves the right to alter, update, or substitute build components and specifications at its discretion, without prior notice or obligation. These adjustments may be made to help customers meet specific timelines while maintaining the highest standards of quality, durability, and efficiency.

Returns:

*We accept returns within 10 days of receipt, as long as the transmission is in like-new condition and has not been installed. Please note that a 25% restocking fee applies, and customers are responsible for return shipping costs