I've been trying to Gold the first Trevor mission, which is pretty easy up to the point where you have to kill all the fleeing bikers towards the end. There are usually four of them, but they split up and flee in opposite directions. By the time I've gunned one group of them down, the other has vanished off the map and the "go back to vehicle" message appears.
This mission really messes you up by making the bikers disappear in such a small window. The one time they fled in the same direction, Trevor was right on top of them when they just popped out of sight. Any suggestions? This is doing my head in.