16 bucks for a gallon (4 quarts) here

Amsoil all the way, all fluids on my coupe. Except for OIL, only German Castrol. six years old and not a single problem.

Personal experience, I had a friend with an 05 coupe that we changed the trans fluid to generic dex whatever its supposed to take after the transgo install, after 2 weeks it was slipping and acting weird, switched back to nissan matic and it worked fine. Could've been a fluke but was enough to scare me into only using Nissan fluid in mine and no complaints so far.

Do you have any real proof either way?

I run amsoil atf with lube guard added to it, a trans cooler, external filter, tuned tq manament map with very firm shifts, and stillen vb. Been running the Amsoil for 2 years with no issues only benefits. No more bangs into first when at low speeds and quicker shifts. Lube guard has something to do with it tho (friction modifier).

I am a cammed vq35de with full bolt ons with Nitrous with small low end hit and 3k 150 wet shot on methanol injection to 7400 ( usually shift at 7200). Been running n2o off an on for years from 50-75 dry (tuned map) shot at fiDDrst for 2 years to 1.5 years at 100 shot to current setup with 130k on the stock bottom end (105k or so off and on spray). Currently making mid 400's whp and tq.
I drive in manual mode which people claim is bad for it (lol) 100% of the time for 105k miles and drive it very hard daily.

I am just posting my personal exp. My trans is holding up very well and since amsoil atf and lube quard (again wouldnt run this fluid without) it has never shifted as well. No slipped logged in osiris.

I would never run again without lube guard or some random fluid... Personal reason for switching was strange shifting when switched to S matic. I waited too long to change the fluid and it was prob too much fresh fluid... I added the old fluid back and over 10k miles switched to 100% amsoil atf with lube guard (2 bottles of the black one I THINK I'll have to double check the bottles).