Check if filemant is not twisted. I had the same problem and it was caused by filament badly coiled on the spool. Try unwind as much as you need for the print, straight it and roll back to spool from front (it's important - do it from front, not from side to not twist it again). And try if it's working.
Notice that head gets filament strainght from front. When sbd roll it from side -like everybody is rolling seawing thread- it may be twisted along it's axis. Plastic is not elastic enought to compensate it during printing and after some prints pressure on it (between spool and gear in head) is big enought to disrupt normal work.
I have several problems with head but all of them was caused by me (when removing filament, wrong temp, etc). But that was only one case when everything was working correctly and stopped "just because". And it was that.
And there is no need to correct pressure on motor gear - everything was working, so that was set up correctly.
But it's only my opinion.
(my twisted plastics: Plast-Spaw Wolfix PLA 1.75mm, red and green; except that "feature" it's really nice material).