But there are also many autobahn kilometers where trucks aren't allowed to pass other trucks or cars.

It gets ugly if someone decides he wants to travel less than 90km/h because truck drivers are always late and always have to drive the maximum allowed speed or their truck will explode.

Overloaded trucks on steep hills also a problem; They are underpowered and thus drive like half the speed they could.

I think the biggest issue with blocking the middle lane in Germany is, that many people can't pass someone in the middle lane because the left lane is too fast for them or at least you always have to suspect someone flying in with like 300km/h