This is what is recommended for most Duramax power steering pumps, I have used ATF but have switched to it, yes it is expensive but the pump is quieter and don't cry like that I'll use this.
Optimized BlueDevil Power Steering Leak Stopper
9 Review
🔧 TRIAX Powerfluid 450: Lifetime Fill Power Steering Fluid, CHF 11S, CHF 202, CHF 7.1 for European Cars | OEM Grade | Hydro-Pneumatic Suspension (1 Quart)
7 Review
🔧 Genuine Nissan Parts - Factory-Certified Catalog Part (999MP-AG000P)
6 Review
LIQUI MOLY Oil-Verlust-Stop, 0.3 L
11 Review