Hi there.
First of all, I don’t think your issue has anything to do with the LaserGRBL.
That sounds to me more like a faulty “wheel” on the carriage holding the laser module.
We had some posts about this in this forum:
…and…
For best engraving settings, try to create yourself a test grid - you can find plenty of these on the web and on YouTube.
Basically, it’s a grid where you mix speed and power to draw filled squares.
Based on these 2 variables, you’ll find the best values for your engraving.
Search the web for “laser engraving test grid”
Note that you should run these whenever you have new material so you know what to expect.
There are also the same type of grid for cutting - instead of using lower power to fill in a square, you have higher power and try to cut the square instead of filling it.
Cheers!