Lots of LSMG will set the machines back to the factory defaults. Some do better than others. Makes a lot of people I know crazy, because when they get it back they have to fix what the LSMG "Broke" for their type of work.
*Keeping in mind, I don't know your machine in particular...*
It's possible he adjusted your upper tension or the bobbin tension too tight or too loose. This would throw the Superior recommendations off a little. That's why they're a starting point.
I mentioned in another thread today that the one FMQ foot I was using on one of my machines causes skipped stitches. I haven't figured out yet what's doing it, but changing nothing else and just changing to a different foot stopped the skipping. There are more reasons than needle and thread. Tension, something wrong with the foot, I found that one of my machines skipped if I practiced without batting, or really thin batting, but was fine with thicker batting. That was somewhat resolved with greater tension and speeding up, but not completely. I should note here that almost all of my practice is done with truly crappy thread. The thread I get on bobbins when I buy vintage machines. It doesn't get cheaper than this. The last thread I used was so "hairy" it looked like wool. The machine didn't care.
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How does it sew for normal piecing? Is the seam good? A little loose? Tight? How does the tension balance look?