Good quality atf fluid and smf with have extra roll over noise its harmless. If it starts to growl get worried, or if you find needle bearings coming out of the oil. Only had that happened once and that transmission is still in a pickup.

 

Romel7 or romel77 in this forum has found and posted manuals that specify 30wt gear oil. Back when these trucks were new and maxed out regularly for a local construction company they had more than one zf5 seize shafts on interstate trips. After switching to 30wt, it was not an issue.

And yes, the company that is making a multi-million dollar contract to build transmissions for a company who says give me something that can use atf, is going to make it work, is it the best thing? I honestly don't think it matters but as things wear and loosen up a bit heavier oil couldn't hurt. Heavy duty trans use oil, decades of trasmissions before the zf used oil, my zf will use oil.