I'll echo what's been said - good quality thread like Sulky or Superior, Metafil or Metallica needle, slow down, and you might have to loosen the tension a bit.
Another option if you have trouble with metallic thread is one of the trilobal polyesters in a color that looks like silver. I've used some called Metrosene and another Poly-X. It's shiny although not metallic, but I find it runs with fewer problems.