I found a SnowRunner gearbox today (that's the name of the upgrade not the name of the game), which provides me a real nice upgrade in a Low+ and Low- gear setting in addition to standard Low gear, which have some pretty obvious use cases that I completely understand. However, I now also have a high gear setting separate from automatic. My initial thought was that this should be used after automatic reaches gear 4, but whenever I shift into high, I slow down pretty dramatically, so I feel like that's not it.
When, if ever, should I use high gear? Or should I pretty much just be using Automatic and Low+?