Whenever going uphill or downhill, drive your automatic car in B (often referred to as braking, which keeps your engine at max in second gear). S is often called sports, similar to D, which is used when you need instant acceleration where generally car maintains higher RPM before shifting to another gear.
I've been to Monal with my 1.0l vitz 2007, without any issue, and kept the car in B on steep slopes. There's a general misconception here that CAT is blocked and should be cleaned. For its self cleaning, you can drive the car to 100-120 kmph in S mode; otherwise CATs are designed to work normal for 80-100k KMs, or even more