I've just installed a "Lite" with the latest i3 MK2S extruder to replace a MK8 on my i3 clone. The MK8 had worked well but had given problems with jamming on long prints with PLA - ABS worked perfectly. The Lite worked perfectly to start but gave the same problem - aagh!!! Given that two completely different extruders/hotends were malfunctioning in the same way I had to look for a common factor. Unlike the MK8, the Lite has a long run between the stepper and the hotend. Typically on the MK8 trying to remove the filament after a jam resulted in it breaking as it entered the stainless steel tube. On the Lite the second time a jam happened it was possible to withdraw the filament and this gave the clue to the problem. The filament that would have been inside the heatsink and PTFE was in perfect condition but the filament that was near the drive gear was heat affected. I had been overdriving the extruder stepper motor (DRV8825 stepper driver) so it was getting quite hot and after a period it and the drive gear were heatsoaking to the extent that the drive gear was softening the filament enough that it was not pushing through the nozzle. Turning the drive current down has completely solved the problem.