When I run into this I get the filament out by taking the whole thing apart. 
You are very likely experiencing what has been called “heat creep”. Heat creep is typically is not a problem in ABS, however. It is a more typical problem in PLA. ABS filament is less conductive and has a sharper melting point than PLA.
The real problem turns out to be the ineffective heat sink fan. I built a new duct and replaced the little blower with a 25mm fan, and all my PLA heat creep problems vanished.
You can replace the little fan with a 40mm fan and duct like they use on the new Taz6 it you like. This solved all of the heat sink cooling problems:
https://devel.lulzbot.com/TAZ/Mangrove/photos/Mangrove_Photos/mangrove_toolhead.JPG
Here is the link to the stl print file:
https://devel.lulzbot.com/TAZ/Olive/production_parts/printed_parts/heatsink_fan/heatsink_fan_duct_v0.6.stl
Here is a link to my duct design that uses a smaller 25mm fan, (I figured this one out just before they came out with the TAZ6):
http://www.thingiverse.com/thing:1461335
Bill D.