Before I did that I was trying to figure out why is unidirectional, always in the same direction, Y axis and shifting up. It was 2-3 times harder to move along the Y axis than it was the X. Seemed weird since I never had this issue until recently. I loosened the y-axis NEMA a bit, and it immediately moved more freely.

Added grease, prints like a boss.

I need to try some of the mods eventually... only thing is, it prints so well, I kind of like it being stock. I may make a reprap and use that as my screw around machine.

Thanks for the help guys!

If it was a heating issue I think I'd have run into it already since it has already seen one summer and it is kept well ventilated.

The electronics can overheat quite unpredictably.  Mine worked great for months until the boards began to overheat consistently.  Then I just added a fan, and it worked perfectly.

It is a very simple mod to try out, and definitely worth it.  Had I known that could be an issue when I was troubleshooting, I could have saved 15+ hours of work.

Also have you checked the stepper driver voltages as they can change over time especially with temperature changes.

I was messing with some of the settings, but reset to factory to rule that out as a cause.

I am still running the one step installer off the site (fresh install for troubleshootings sake). Everything is completely stock from SD. I have greased once, but everything is sliding fine, nothing broken...

If it was a heating issue I think I'd have run into it already since it has already seen one summer and it is kept well ventilated.

What's happening is about 2/3s the way through a print it is stair-stepping upwards. It always happens at around 2/3rds of the way through a print. If it is 3mm tall, or 3 inches. It also appears that the larger the print, the larger the jump.

I am totally lost on this one.

Anyone got any suggestions?

White lithium grease.  I have been meaning to try silicone.
Just clean with a cloth or paper towel.

NO! Don't do that. I tried silicone and it seemed to gum-up after a while and made things worse. Stick with the while stuff.

I will remember this one.....

The gaps could either be a weird slicing or model design issue (scroll through layer preview in RH to see if the gaps are present in simulation), or they could be from backlash.  Backlash can be treated with the perfect circle alignment procedure from Solidoodle.

Now, if you look closely you can see some kind of "gaps" in the print, so I am not out of the woods yet, but this is huge progress.

Ian Johnson suggested if Z lift helps, I may need to print a "Z Nut Hugger" and that'll help more than the Z lift does.

I'm feeling very encouraged that there's progress.

Set that parameter to a large distance like 1mm just for testing purposes.  Once you figure the problem out you could tone it down, if it turns out to help.

Every single skip seems to correspond to a moment when the extruder is about to make a long move, often between layers, or between distant parts of the same layer, and every time, it "bumps" into a part of the already-made object on the way, usually right near the beginning of the long move.

I still have to try lithiium grease after I have a chance to buy some.  There is also the stepper motor thing that Solidoodle Support would have to walk me through, though I don't know how likely it is it could be something like that given the symptomology.  Otherwise... what's left to try?

Later today I'm going to try loosening and doing a few more attempts at a test.  Since it takes about an hour to get the bed up to temperature for each test, trial and error is a very slow method of solving this, but it's all I've got.  I'll probably pick up some grease after work tomorrow.

http://www.thingiverse.com/thing:38952

The belts running in the y direction should be surprisingly loose.  The y belt in the back bottom left hand corner should be quite snug.  The tension gauge gives you a starting point and empirical data that will let you work your way towards the sweet spot for your doodle.  It seems frustrating, but will be fixed in short order if you take your time.

Do grab some grease and make sure the rods are well lubed.  Also, the fan on the board will always help, so I would suggest continuing to use that even when you solve the belt problem.

I tried a print yesterday with a fan pointing at the board.  Not only did it still do a jump, it did a bigger jump than it has ever done before, like 2 centimeters (not millimeters, centimeters) right after the first jump.

What changed to cause this?  Easy.  Having been told a jillion times to adjust the belt tightness, without being told how much is too tight or too loose (I even posted a picture trying to demonstrate how tight it was and no one responded), I tried adjusting it to tighter.  It ended up way too tight; I could tell because the motor wouldn't run and made a terrible noise.  I then tried to loosen it and one of the screws went a bit too far and came out of the nut.  I then spent about an hour trying to find a way to get it back into place before I finally found one that worked.  I tried to adjust the belts back to about as tight as they had been before this experiment, but clearly they're wrong in whichever direction they were before, only more so.

So I'm thinking the problem is probably something to do with the belts, but since no one can tell me how tight they should be (beyond the entirely unhelpful direction of "just right") I don't see much chance of me just happening to stumble on the right tightness.  Someone told me in IRC that it doesn't really matter that precisely how tight they are, just that it be balanced, but I don't know what else would explain why it's suddenly making far worse jumps than it was.

(I still haven't tried the grease, though.  I have to stop and buy some next chance I get.  I suppose it's possible that it got more ungreased during my efforts to reattach the belt.)

Could be the extruder nozzle hitting the cooled plastic and its getting stuck or they didn't tighten one of the screws on the rod or something.