Good analysis Christuna, especially about the forces involved with shifting into park while still rolling.
Fun fact: At a 45% gradient (25 degrees), Waipio Rd. in Honokaa, HI is the steepest road in the USA. Here are the top ten:
https://cdn.fixr.com/infographics/top-10-US-steepest-streets-1.jpg
Baxter Street here in Los Angeles is a real eye opener to first-timers when Waze routes them around freeway traffic, lol. Waze really shouldn't use Baxter.
https://editorial01.shutterstock.com/wm-preview-1500/9689883a/4ee71eb6/steep-street-los-angeles-usa-shutterstock-editorial-9689883a.jpg