Mishimoto Transmission Cooler - Chevrolet/GMC Duramax L5P 6.6L 2020-2026

The Mishimoto Transmission Cooler targets the factory cooling shortfall on the Duramax L5P 6.6L, where fluid temperatures climb fast under towing and heavy load and heat is what wears a transmission out. The tube-and-fin core adds 245% more core volume, 137% more frontal area, and 173% more external fin area than stock, giving the system far more capacity to pull heat out of the fluid and hold temperatures in a safe range. All-aluminum construction handles the demands of stock and modified trucks, and the cooler reuses the factory transmission line connections for a complete bolt-on install with no adapters or extra plumbing.

Specifications

Documents: Installation Instructions (PDF)

This part fits:

Shipping

• In-stock orders placed before 3 PM EST ship the same day — everything else ships within 24 hours.
• Standard, expedited, and overnight options at checkout.
• Oversized items ship by freight and take longer.
• Backordered items ship as soon as stock lands — contact us for lead times.
• International orders: prices do not include VAT, duties, or import fees. Your country charges these at import and they are the buyer’s responsibility.

Returns

• 30-day returns on new, uninstalled items in original packaging with all hardware.
• Standard returns: 8% restocking fee, buyer pays return shipping. Both waived if the item is defective or we made the error.
• Installed or used parts can’t be returned — confirm fitment before you install.
• Special orders and custom items are final sale.
• Email us for return authorization before shipping anything back.

Full details: Shipping Policy · Refund Policy