Fluids - Information, Suggestions, etc.

[Simplicity]

I'm preparing to change all the fluids in my bus, so before I did, I thought I'd reach out and ask for input.

The feedback doesn't have to be specifically about my setup, but if there's any particulars to consider, I'd appreciate knowing.

I run a T444E (190K) with an Allison MT643. Here's what my plan is at the moment.
Oil - Shell Rotella 15-40w conventional.
Transmission - Dexon III or C-4. Most likely C-4 because it's a four speed with a wide range, I want to provide as much protection as I can.
Power Steering - On my power steering reservoir it gives me three brands. I can find a current day GM 1050017, now 89021182, yet I'd like to be reassured that the new stuff is still compatible.
Coolant - Good ol' regular green.
Additives - Fuel, HotShot was recommended by a diesel geek friend. Not sure if the tranny or coolant (SCAs) benefit from any additives.

I'm also going to send in my motor and tranny fluids to be tested, Blackstone probably, but if you've done this testing and have recommendations, please let me know.

I know with older engines and transmissions there can be some issues with newer fluids and all the additives, so I'm trying to stick pretty old school.

What have you used? What do you like and why?

Thanks in advance!