I live in a hilly but not mountainous area. Today I came to a stop light next to a late model semi. His clutch was smoking. I could smell the burnt smell a mile away.
I was tempted to knock on his window and tell him. I just realized how many trucks I have noticed who have burnt clutch odors eminating from their vehicle.

My question is why is the clutch burning. Is it driver inexperiance? lazyness? poor maintenance?

I am not a trucker but when I was younger I've gone through several clutches. I also drove a vehicle for a while with a ceramic clutch(no slipping with those).

Are the drivers slipping their clutches climbing the hill or has it something to do with them going down the hill?

Another question is the clutch burning something to do with range control shifting?

Are there reason's that aren't always obvious such as some kind of clutch brake that would cause burning when coasting downhill in neutal?