You're right, all the new software runs really fast. You might also have a problem with the heater not contacting the nozzle enough which can cause the under-extrusion, or you might also have the wobbly feed gear problem.

The 1.3.4.1 software just came out on Wednesday but already they finally, FINALLY discovered the bug that was causing all the endless layer shifting. They say a fix will be out on Monday and it is related to the backlash compensation being overly aggressive and trying to move the head too fast, causing it to miss steps.

I agree totally with the battle with always going back to 8.3, but being annoyed that you miss out on some good features, like accepting external G code, Z-hop, retraction and wave bonding.