Autobello Stambecco rock crawling issue

This one was really frustrating until a random search around YT. There's a mission in Johnson Valley that specifies you use the Autobello Stambecco to rock crawl. To my surprise the vehicle was wholly unable move very far starting on a hill. It wasn't until after quitting many times I found a video that explained to crawl you need to barely press in on the brake while giving it gas. No brake = no crawl.

My question: Is there a mechanical reason for this? Additionally, why would the map creator chose this vehicle and not let anyone know there's something very specific and unintuitive you need to do to even have a chance at finishing this mission?

 

At 3:28 in this video the author describes perfectly what's happening (). I noticed it with the Rally Stambecco crawling mission and the Fully Loaded Dually Gavril crawling mission. Both of those trucks you hit the gas when trying to crawl/hit a steep incline, the tires will lose grip and you'll instantly jump from N to 2 or higher, but if you tap the brake to bring it back down to 1 gear, you'll catch traction.

Guessing this isn't an issue with the manual option?

Any help is appreciated.