I just purchased, off the internet, a new Spectrum 2-8-0 DCC equipped.  It runs with jerks at slow and start speeds.  Nothing noticable at higher speeds.  I have broken it in, both in reverse and forward for 1/2 hr each at high speed.  No change to jerky operation.

Could this be the decoder or as proposed by a club member, the rods are not in perfect alignment or a broken gear?    I visually see no issue with the rods.  I know it is covered by warranty, but if I can solve here I will save the $10 shipping.  Anyone else experience this problem?  Thoughts welcome.