Transynd (Allison's Severe Duty) Transmission Fluid
For 2001-2019 Duramax with Allison 1000 Transmission
This TES 668 fluid is backwards compatible with TES 295 fluid

Castrol TranSynd 668 is a premium, full-synthetic automatic transmission fluid specifically formulated for Allison Transmission® on-highway automatic transmissions. TranSynd 668 provides oxidative stability, anti-wear performance, and friction durability, as well as TES 668™ specification differentiators such as extended anti-shudder durability and extended clutch friction durability. This fluid features an Allison TES 668 approval. The TES 668 spec is fully backwards compatible for TES 295® applications.

Features:

• Delivers improved gear protection.
• Delivers extended anti-shudder durability.
  
• Delivers extended clutch-friction durability.
• Excellent corrosion and foaming resistance.
• Excellent thermal and oxidative stability that helps to prevent deposits and oil thickening.
• Excellent transmission cleanliness under all conditions permits extended oil-drain intervals and decreased
  servicing.
• Excellent temperature reduction through reduced friction leads to longer oil and component life.
• Outstanding cold-flow properties enable faster oil flow to all critical components, particularly during cold starts.
• Optimized frictional characteristics gives smoother gear changing at all ambient temperatures and load
  conditions.
• Excellent shear stability properties help to retain full transmission performance over the entire oil-drain interval

Documents from Allison: Brochure, Characteristics