4AT got L gear? Mine is CVT, go up genting few times. I only try L gear once, car basically can't move fast, very high rpm. Go genting no need to use. I use D all the way up, tried once using sports mode but D mode is actually better. Sports mode car accelerate up slope slower, rpm remain above 3k and will increase a lot when you step more. For CVT, rpm can remain at times but car accelerate, just like normal driving, less stress with this mode.
Any 1.5L sure can go up genting. If CVT even better, maintain rpm to provide max power at any speed. No need to gear hunt.
Down slope use sports mode, car can maintain speed, if D mode car keep accelerating, dangerous and harder to brake. This is for the steep slope part.
Sidetrack a bit, I was surprised on my first drive down, the first expressway where there are many long slopes. It's the first time I experience another good point of CVT, when driving at 80-100 km/h on the long down slope, car downshift automatically, rpm increase and car maintain speed, no need to step on brake at all. On SG roads I never experience this.