I don't think the upgrade caused it, I'm thinking some other adjustment he made has changed the way it sews. Thought I better follow up with an explanation of what I meant.
Cas

----- Juddered!

I never used to have trouble sewing with it. I made a purse and sewed through double layers of Jean weight denim, with batting and quilted lining, which was six layers, doubled at some seams.

Now, it balks at a meager patchwork seam, quilting cotton. It's been that way since I had it upgraded.
Cas