[Jason]

[EDIT AGAIN] now that I have the full game and went through training I found out you press V to go into sneak mode, TAB toggles between the default run and walk modes - holding shift does the same

[EDIT] I was able to get him as he turned around. Punched him out. Thanks for your help.

I believe it is on, I made sure by checking the speed of the walk. I'm at a bunker - there is a guard outside that doesn't like to be snuck up on and the guy in the bunker at the bottom of the stairs that is doing something to a tyre turns around as well (so yes the truck driver). I am playing the demo at the moment, just ordered the full game, could it be the demo?