QTR-Quadtone RIP

I have for many years been printing with Quadtone RIP on my Epson 1440 at a (maximum?) dpi of 2880. I have just recently purchased from Epson a 1430 as a back-up printer. When printing initial test photos on the 1430 I noticed what is perhaps termed "laddering" (narrow lines) on about 10% of the edges (top and bottom in Portrait mode, left and right in Landscape mode) in the direction the print head moves. Thinking this was perhaps a problem with the new printer, I went over some reasonably extensive testing with an Epson tech rep on the phone and determined that the printer was working fine. He opined the problem might be with my printing software. I then ran another test print with QTR, but changed the dpi to 1440 -- and the print turned out fine. I do not understand (yet) all the relevant terminology, so I'd be most appreciative if someone would explain to me (1) the difference in meaning between the two dpi settings, (2) the possible reason for this difference between the two printers' outputs, and (3) what possible loss in quality I might experience by needing to use the 1440 dpi setting with the 1430 printer. Many thanks.