I'm not trying to be combative....but I find it a little humorous when someone says "Redline MT90 doesn't do crap for these"........When Jerry has specifically stated...going back a couple years...that the only Redline to use is "Redline MTL" that is GL4 and is the only Redline that helps.
If you're not using what he specifically stated helped, and helped mine, I'm not following how you state this fact it doesn't help. Not looking at the other data, you're specifically saying this doesn't help I'm trying to understand how you know this.
I own 3 NSG370's right now. One in my black 2005 would grind 1-2, 2-3, and 3-4 often. Not reverse, but who cares the dam thing would grind. MTL helped immensely and 1-2 still would grind so I got it rebuilt.
The other 2 a Silver 2005 and a 2008 JK both have the NSG and have MTL and shift like butter. I have zero issues with them 1-6. The 08 had some, and none now with MTL.....100% anecdotal....agree...but I switched based on someone providing a lot of experience.
If your Tranny is toast....nothing helps. And if someone says "Leave old stuff it new stuff ruins trans" I just don't listen, that's nonsensical (not saying you said that).