What are you using for oil in your 4 speed?

I have a 1971 833 23 spline 4-speed 340 car. My trans up shifts great, but have a tough time down shifting. I am currently using 85W-90 gear oil compatible with brass stop rings. The coldest temperature that I would drive it would be 50 degrees and the warmest would be 90 degrees.
I was wondering if auto trans fluid would make it down shift easier.

I used to run Gear oil in the summer and auto transmission in the winter and occasionally a mix if the shift wasn't to my liking.

The old 833's like a good fluid but are pretty flexible.

Redline 75W-90NS synthetic.

I think I've used 85W-90 once year round, I just switched back to 85W-140. Below freezing it's like trying to stir molasses? until the trans warms up some. But it still shifts fine on the road. I put 37,000+ miles with RedLine 75W-90 NS. All that being said, I've never noticed a significant difference between any of the fluids. It might shift "better" now with the 85W-140, maybe I don't know how to drive

. If it up shifts okay but hard down shifting, the brass rings are probably gone and need replaced. Auto transmission fluid will make it shift easier, if everything was okay before you put the ATF in. If everything was not okay, then I doubt it will make a difference. If you want to try a different fluid, try 2 1/2 qts of regular engine oil. Maybe like a 30 weight. It is GL 4 like ATF and syncro oils.

This is correct.

Pennzoil Synchromesh.

85W-90 here. No problems and smooooth shifting!

The tired (I guess) 833 in my road runner did not shift as silky smooth as I would have liked when using 90 weight. I put ATF in it and it made a small difference. It did leak slightly with the thinner ATF though.

I tried Amzoil synthetic in mine and it would not shift well at all. Went back the the lighter 85-90w and it went back to shifting fine.

I use the oil Jamie Passon sells in my 833 4-speed

RedLine MTL
https://www.redlineoil.com/mtl-75w80-gl-4-gear-oil

I've been running 85/90W GL-4 for the last 42 years in my Challenger T/A.... I change it out about every 10 years

Another vote for Pennzoil Synchromesh here.

StaLube 85-90 GL-4

Another Pennzoil Synchromesh user . But when I ONLY want Mopar Fluid in my MOPAR's the Manual Tranny Lube Part # 0487446AB also works Great , just like the Pennzoil .

Same here.

I've been using MTL for years in my Coronet. Seems to work okay.

Pennzoil synchromesh in the my dad's 4 speed six pack road runner. Works great.