Originally Posted by QuiltE

We pay so much for these machines, why cheap it with cheap needles and thread?

However, keep in mind it is not all about the needles and thread.
The fabric and batting used create different situations, requirements and effects.
Also too, tension and machine settings have an effect.
Knowing your machine is important.

Perhaps the best step to resolution would be to take your machine to your dealer along with a show and tell (aka samples) of what's happening. Stitch there in front of him/her and get some help!