Our clubs new layout has a 3.125% max grade. We haven’t had much of a problem yet. My new VL Challenger though won’t pull 9 21” passenger cars up the grade it just stalls and slips. No problem with the older challenger or big boys.
here’s the older challenger with a 36 car train
https://youtube.com/shorts/SeRXuVCX8RU?feature=share
heres more on the layout