After printing great for awhile now. We have gone through 4 hot ends last week. After changing each we do a z offset, bed calibration and then a fine tune. After getting everything ready to go. The printer primes itself, and start in on the raft. After 2-3 layers which looks good the PLA jams in the extruder and the feed gear start to skip. There is plenty of z offset and by no means is it to close to the print. Also cleaned the spline gear and everything seem to not be binding. Any ideas how i can fix this?