My glass is (was) sliding around as well. I just noticed it when watching some support material be printed.
I shimmed the front right clip with some silver anti-static material, but I suspect some either some printed shims or cut silicone rubber shims will be a better fix.

Shimming with paper worked for me as well. I used some heavier paper that was hard to slide in, Y-dimension accuracy is on par with X, and cylinders are coming out well.
Thanks!

My prints with different speeds (different profile speeds in s3d; the slower was at 800mm/s for print speed and 2000 for XY movement, the fast was at 2200 for printing, and 12k for movement) didn't' show significantly different results from eachother, nor improvement from my last print. I've used PE...

What slicer software are you using? I'm using Simplify3d.

I tried lowering the xy jerk to 1, but the issue is still present. I'm running a test print with two different speed settings to see if a lower speed will improve things. It seems like the Y axis is lagging the X just a bit.

I have the same issue as well. It's subtle most of the time, but shows up on cylinders especially when it prints the inside and outside in different directions. My calibration cubes also show a bit smaller in the Y direction. I've tried tightening the belts, mounting, checking the pulley lock nut lo...