Y axis skipping (2 replies)

Ok. I have been running my prusa i2 for a while now and have an odd problem. The y axis appears to skip on longer prints, but not all of them. I am using white lithium grease on the rods, and it even does it right after I disassembled and greased the bearings. I am considering adding code to the g code to home the axis every several layers to help correct any alignment issues.

Does anybody have any suggestions on what else might be wrong?

I am using marlin firmware. And when the prints finish without skipping I am happy with the results.