wouldn't a gear oil allow faster shifting then ATF? ATF to my understanding has alot of friction modifier so the sycros would take longer to come up to speed. but having all the friction modifiers plus the fact ATF can handle alot higher temps should result in alot less wear.
but dex111 is roughly 10w-20 grade oil and is more on the hydraulic oil side of things, gear oil being thicker, is more clingy and generally dosnt run back as quick, keeping bearings that are splash lubed, lubed longer then thinner oil, the thinner the easier it is for it to squeeze out of componenets, eg, synco etc etc, as such, makes gear shifting easier, syncros brake the surface of the oil quicker, make contact and brake quicker, but at a cost of not protecting the internals as well, but, thats what ive been told by mentors of mine, guys with the expierance, ive learnt from....
really i go by whats recommended unless a dealership can give me a document showing a superceded spec, ill go by the manufactores spec in the book, eg, the tremec box is rated for atf, some rodeo gearboxes are recommended for regular engine oil etc, etc,
monaro, not doubting what the dealer has said to you, but i wouldnt be surprised if the dealers you rang think the v6-v8 boxes are the same, too many times ive talked to someone at a counter or ill informed worker and they've given the wrong spec or information