Reprap Failing last part of build

Hi, i have a reprap mendel, For some reason whether its a large or small object im making on the last few passes of the part it starts skipping and begins to lay down half on and half off the top of the job.
any idea why this is happening? ive slowed down the travel speed between layers so the motors are not skipping an loosing its position but it stil happens.
Any help appreciated. Im using the standard software they recommend so pronterface and skeinforge.

Also what other software is there that are more customizable? f

Cheers

Nick

you could use slic3r, but any package should have a cool feature to slow down speed at top of print if print area is small. can you provide an image?

it also could be that your z rods your bushings slide on are not perfectly strait, loosening the belt tention as you travel further up the z axis. it is hard to know what is going on without seeing an image or video.

Check that the motor current settings are correct and that there's no binding on any of the axes - as mentioned, a picture would help

I'm not sure you'll find anything more customisable than skeinforge!