I found these: http://www.ebay.co.uk/itm/3D-Printer...lfvZl0hAxmaP-w

Will solve your problems. They provide a much better grip onto the filament than the standard ones do. Just check these will fit your extruders, but I think they will.

You will find that ABS does not jam as much, as it is less soft. Increasing the hot end temp feels like the right thing to do, but it may just make the filament softer further up, so will actually add to the problem.

Make sure you clean all the gunk off the hobbed gear, as if this builds up slippage will occur.