When the Dexron III licences expired in 2006, GM moved users onto Dexron VI.

A potential issue, though, with using Dexron VI is that its viscosity (new) is lower than that of Dexron III. Not necessarily a good thing if your valve blocks are worn, which is a particularly common issue with the 5L40-E! The justification is that the better shear stability of Dexron VI means the viscosity remains at its design specification for longer i.e. after a period of use it will be higher than ‘worn out’ Dexron III.

Someone on another forum asked if I thought a fluid called Texaco ATF HD 389 might be a more suitable alternative than Dexron VI. It has a kinematic viscosity of 7.1 mm²/s at 100⁰C and 34.9 mm²/s at 40⁰C. This compares to 7.4 & 33.8 for the original Texamatic 7045E fluid and 5.8 & 29.5 for Dexron VI so, on the face of it, it would seem a more suitable replacement for Dexron III than Dexron VI. Just my opinion, though.

Phil