lines and splotches on double sided prints

[LanaBell]

When I print a double sided print, or if I print multiple copies of a document that isn't double sided, I get lines and streaks and ghost printing left on my prints.  If I only print one page, one sided, it prints fine.  Or if I need more than one copy of a document, if I print one, then print a second copy instead of sending two copies at once, it prints fine.  It's got me baffled and this is a new printer, just purchased in July.

[Repairatrooper]

Can you post a sample. Might be as simple as a wrong media type setting which prevents the fuser from getting hot enough during extended print jobs.