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Mishimoto MMTC-DMAX-03SL Trans Cooler for Duramax 6.6 LB7/LLY 2003-05

  • Based on 69 reviews
Condition: New
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Availability: In Stock.
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Arrives Sunday, Oct 25
Order within 22 hours and 23 minutes
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Features

  • Direct-fit for all 2003-2005 Chevrolet/GMC 6.6L Duramax (LB7/LLY)
  • Stacked-plate construction for maximum durability and superior cooling
  • CNC-machined adapters make it easy to connect Mishimoto cooler to stock fluid lines or AN lines
  • 174% greater core volume than stock cooler & 192% greater external fin surface area over stock cooler
  • Mishimoto Lifetime Warranty

Description

There's no greater enemy for a transmission than heat. Whether your 2003-2005 Chevy/GMC 6.6L Duramax is a dedicated tow vehicle, hardworking fleet truck, or a daily driver with a liking for the drag-strip, you need to ensure that your transmission runs cool. Luckily, Mishimoto has developed a direct-fit transmission cooler to do just that. Our 2003-2005 Chevy/GMC 6.6L Duramax transmission cooler utilizes a stacked-plate design for maximum durability and powerful cooling. Aside from it's durable construction, this transmission cooler is significantly larger than the stock core. The Mishimoto transmission cooler boasts a 174% greater core volume, and 192% greater fin surface area than the stock 2003-2005 Duramax transmission cooler. The included CNC- machined adapters connect directly to the stock transmission cooler lines for leak-free cooling. Direct-fit brackets and tailor-made hoses make installation easy. Like all Mishimoto products, this transmission cooler is backed up by our Lifetime Warranty with Accident Protection for worry free cooling as long as you own it.

Size: Stock


Brand: Mishimoto


Color: Silver


Item dimensions L x W x H: 29 x 4 x 14 inches


Connector Type: Adapter


Exterior Finish: Smooth


Item Weight: 9.3 pounds


Number of Pieces: 1


Global Trade Identification Number: 84


Manufacturer: Mishimoto


Brand Name: Mishimoto


Number of Pieces: 1


Model Number: MMTC-DMAX-03SL


Global Trade Identification Number: 84


Manufacturer: Mishimoto


Manufacturer Warranty Description: Lifetime Warranty


Unit Count: 1 Count


UPC: 811580034084


Included Components: transmission cooler


Item Type Name: Transmission Cooler for Chevrolet/GMC 6.6L Duramax (LB7/LLY) 2003-2005


Manufacturer Part Number: MMTC-DMAX-03SL


Size: Stock


Item Dimensions: 29 x 4 x 14 inches


Item Weight: 9.3 pounds


Connector Type: Adapter


Color: Silver


Exterior Finish: Smooth


Frequently asked questions

If you place your order now, the estimated arrival date for this product is: Sunday, Oct 25

Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

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Leasing options through Acima may also be available during checkout.

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Top Amazon Reviews


  • great design
Fits perfect, easy to install with NO extra parts needed. I didn't have problems with temp, just upgraded so cannot comment of temp difference however more surface area and more coolant is nice assurance.
Reviewed in the United States on September 30, 2025 by Paul

  • Works for me maybe 20 degrees lower shifts better by a long shot
Great addition to a 2500 Duramax runs about 20 degrees cooler than normal doesn't hit 225 anymore just about under 200, quite a bit costly but def works just wished they had a spot for the ambient temp sensor but unfortunately does not fits like it should not problems there just worries me about the cheap hose clamps they sent so I replaced with better ones but seems like the hoses slip maybe cause a leak later, but for now works like expected just need to keep an eye on those hoses. Does block off a little more of the condenser so make sure your fans are functioning as they should, just a heads up ... show more
Reviewed in the United States on September 13, 2023 by Ray Filoteo

  • Great quality
Well made! Packaged awesome! Perfect fit! Put heat on the old lines if there stuck, easy install after old lines are removed
Reviewed in the United States on November 22, 2019 by wendi Bauer

  • A must have for diesels.
I live in TX, so you can only imagine the heat. I installed this on a 2004.5 LLY 2500HD 4x4, temps with normal driving was around 200 degrees on the stock transmission cooler. With this being said, I was not even towing anything. This was normal driving back and forth to work, roughly a 30min drive. After installing this new cooler, my temps decreased almost 50 degrees. I have yet to tow anything in order to give you have a full update I will have to repost then. I would have to say for now this has been a great investment. ... show more
Reviewed in the United States on August 14, 2023 by Stephen H.

  • Worth the extra money !
Old cooler was leaking and wanted to upgrade because I do alot of towing with dump trailer so far I can tell a difference in trans temp 140 towing and 116 cruising, real test be in the summer .
Reviewed in the United States on February 6, 2024 by alex

  • Great Performance
The Mishimoto transmission cooler reduces the transmission temperature by almost 100 degrees. When towing uphill the transmission temp still increases but stays under 200 degrees whereas before it would overheat to nearly 300 degrees. I highly recommend the Mishimoto transmission cooler. It comes complete with all hardware and hoses ready to install. It looks pretty cool too. ... show more
Reviewed in the United States on September 5, 2019 by Rob V

  • Mmmm
No leaks day and night difference
Reviewed in the United States on October 2, 2024 by Branden

  • Transmission runs 30-50 deg cooler
Install took less than an hour, my Allison transmission runs much cooler. Very happy with this product. Worth the $400
Reviewed in the United States on July 19, 2022 by lgriff5958

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