TES-389 is strictly DEXRON-IIIH fluids. I wrote the specification after Allison had Viton seal problems with DEXRON-VI. We wanted to "weed out" any DEXRON-IIIH that had the same seal compatibility issues as DEXRON-VI. The TES-389 specification required proof of a DEXRON-IIIH license plus running of a special Viton seal test. Any DEXRON-IIIH products that passed the tests were granted the TES-389 approval.
TES-389 is not as good at TES-295 fluids. Much less oxidation resistance and tons more viscosity loss. That's why the drain intervals are so much shorter for TES-389 fluids.
