Problem, Prints lean to one side, Fixed

So there is this problem that effected my first printer the Boxed Reprap I called it, the problem was that prints would lean in one direction, always the same direction.  This printer was very large and used the gen 3 electronics from makerbot.  Solution is at bottom.

With help from every one that would volunteer help in the opensource 3D printer world I checked many many different possibilities:
Stepper drivers: I swapped them around, still leaning
Steppers: swapped them around, still leaning
Checked for binding, axes would move very smoothly in any direction
Z axis was vertical

I could not get this printer in the end to print perfectly vertical it was missing or skipping steps, I eventually assumed it was from the print bed being so heavy, since it started when I went to a moving bed setup, and it was such a large bed.

So came Artifex, my current printer Designed in cad to keep friction and weight down made the printer significantly smaller, kept the same build area, and reused almost all of the mechanics except for the ball screws.  This printer is built with the Ultimaker as inspiration.

Prints still leaned, the printer had all new electronics, different bearings different mechanics I didnt understand, even the steppers where different and new.  So I had to continue to troubleshoot.

After doing all of the same troubleshooting again I came upon the cause by accident, it was the computer.  The more cpu intensive work I was doing on the computer while printing, the more the part would lean, stop doing pc work and it would lean less.

Solution: So I printed from SD card, prints leaned less, then I printed from SD card and unplugged from the computer, leaning was gone!

There was so many more things that I tried, but I was so mad at myself for not figuring it out sooner, but without mistakes we will never learn.