DEXRON-VI fluid was required to pass all of the DEXRON-III(H) tests but most of those tests were increased duration but with the same limits. In addition the DEXRON-VI specification contains a number of additional requirements that were not in the DEXRON-III(H) specification. In addition to that further test hours and mileage has been clocked up on both dyno and fleet testing. The durability of a DEXRON-VI 'blend' is typically about two to three times greater than a DEXRON-III 'blend', even a synthetic one.