Is this movement through other trucks in Auf Achse correct?
The 2007 rule book PDF I have says "It is permitted to drive through spaces with trucks." Unfortunately, I don't know where I got the PDF so I don't know if it's an official translation. It has the 2007 Schmidt Spiele artwork though, so could be.

The SpotLight on Games rules translation from 2003 (and thus presumably for the 1987 edition) (here) says "However, it is allowed to pass another player's truck in either direction."

Neither says anything about skipping the space though. I've always played it as the occupied space counts but you may not be able to stop on it. (In 1987 rules, you can't stop on it if there's a truck there. In 2007 rules, 2 trucks can occupy a highway space. You can still pass them even if the space is "full" though, so long as you end on a legal space.)