Weird Z Axis Issues

Good evening,

Had my CTC printer for almost a week now, upgraded the firmware to 7.5, the only problem which keeps rearing its head is the occasional bad layer. Seems fairly inconsistent, like maybe the built platform has moved too far? Sometimes the print recovers, if enough material is laid on top of the bad layer, but usually the print is ruined.

Please help! I really want to believe that this printer is capable of good prints!

Attachment 6465

Have you tried lube on all axis, checking the nut for Z, or printing out the Z axis stabilizer from thingiverse. If the nut on z is loose it could be binding and dropping a few mm as it travels. The extra looseness could also indicate the Z axis screw is loose or warped needing the stabilizer.
http://www.thingiverse.com/thing:496298