Hopefully someone from one of the european countries can chime in on this.

From my own experience driving in Europe in areas like Spain and Germany larger trucks are limited to 80km/h Max and cannot pass each other on hwys. Unless its a very specific section and especially not on uphill sections at all.

From what I seen as well is when one truck trys to pass another the truck being passed drops speed to allow the overtake to happen as quickly as possible allowing the truck to merge back into the far right lane.

Though trucking is alot more regulated in the EU in terms of size and length of trucks and trailers, as well as safety and speed.