Bisher sieht mein Code so aus und das funktioniert (alte pfeilspitze):
\draw [->,shorten >=4.5pt,shorten <=4.5pt] (2,8,5) -- (2,11.5,2.5);
\draw [-{Stealth}][,shorten >=4.6pt,shorten <=4.5pt] (3,8,5) -- (2,11.5,2.5) node[midway,sloped,above]{test};
\draw [->,shorten >=4.5pt,shorten <=4.5pt] (2,8,5) -- (2,11.5,2.5);
\draw [-{Stealth}][,shorten >=4.6pt,shorten <=4.5pt] (3,8,5) -- (2,11.5,2.5) node[midway,sloped,above]{test};