When filament must make a "U" shaped curve (see picture above), using this https://www.thingiverse.com/thing:2462556 it was making too much friction and making the extruder skipping too much steps.
So I decided to make something that would have almost eliminate that friction. First I tried with a little circular pulley, but the U curve was too much tight and friction was still there, also it was stretching filament a little. Than I thought that a more wide curve was better, so I made it oval... and it works! Now filament slides very nice.
I'm a beginner in 3D printing and this is my frist Thing I share with this awesome community. Thanks!
ANYCUBIC Kossel Delta Pulley
Support needed only for the bracket.