If your car is stalling while an off-road hill climb, the vehicle will be in gear with the engine switched on but stalled. If your car loses power while driving up hills like this, it is recommended to perform a Hill Stall Recovery for manual vehicles.
Start by switching the engine off and placing your foot firmly on the brake. You may then depress the clutch and select the reverse gear in low-range. Slowly take the foot off the clutch and off the brake, one step at a time. The vehicle will then be in reverse gear with the stalled engine stopping it from rolling down the hill. After you made sure that the back track was clear, start the engine and keep your feet off all pedals. It will result in a smooth downhill progression.
When it comes to automatic vehicles, simply place your foot on the break, select the appropriate gear and slowly take your foot off the brake.