Velleman K8200 - Filament stops feeding when Z-Axis moves quickly.

Hello

I've have a long standing problem where the filament might stop feeding correctly when the Z-Axis height increases rapidly. This usually occurs later in the print when the extruder is moving up relitively quickly.
When it does stop feeding the gearing will continue to turn normally and a notch will be cut in to the filament. So it seems like as the extruder is moving closer to the spool the tension change in the filament is causing the hobbed holt to loose a firm grip.

To counter this I have changed:
The hobbed bolt http://ooznest.co.uk/RepRap-Universal-Hobbed-Bolt which has the notch aligned with the opening on the extruder.
The Hotend has been changed for an E3d V6 which works well and isn't clogging.
The filiament spool has been moved from the edge of the Z-Frame to the middle of it so that it feeds directly down in to the extruder rather than curving down in to it.

Has anyone got any other ideas of what i can do to deal with this?
My next plan of action was to change the spooler holder so that it actually has bearings on it to reduce the amount of effort needed by the extruder to pull filament from it.