I always had trouble with fluxcore as well. pushing uphill can be difficult without correct wire settings, gun angle, ect.
I feel that a good uphill(3g) method is the upside down triangle method. You can see this here.
http://www.weldingtipsandtricks.com/ver ... nique.html
(this is for mig i know but the concept is very similer)
4g i feel is better to push, this seems to get more penetration, which a weld inspecter will be looking for.
Dragging i feel is more usable in a shop enviornment, where an inspection might be less prone and speed is priority.
best of luck,
-Rick