Sulphur has long been a additive for oil to be used in gears experiencing high pressure and sliding contact such as hypoid sets. Daimler doesn't do anything without cause. I wonder if high sulphur transmission fluid in conjunction with an instruction to purchasers to never change it may have been a factory experiment. I use my tranny fairly hard with gutted converters and extra intake air. Also, I go down through the gears at stoplights as on my motorcycle. I don't tow over the Pass as my last Tahoe went out at 120,000 miles despite the addition of a separate fluid cooler. This was good fluid for me. Factories do experiment like Harley did with OHC drive belts instead of chains (now the norm). If this were an experiment, there are other reasons besides non-functionality which could have caused its discontinuance: EG, reduced profits to dealers for service, the Euro eco-nannies or MPG. Just another one of life's mysteries. I'd prefer not to change every 40k.