3 potentials: 1) crap on your printhead 2)bad alignment 3) dirty encoder strip/sensor.
1) dirty printheads might not be the case, as you've recently installed it and most operators will clean their printheads prior to diagnosing further.... buuut never hurts to clean it again anyways. gunk built-up on other printheads is always worth removing as well.
2) are you certain your alignment procedures were done correctly? I believe nozzle-test prints only reflect mechanical alignment of printheads installed. there are some procedures where you add values, and others that you replace.... and extreme values will simulate overspray when applied to your prints. I once kept adding to a value thinking it would correct the pattern of the test print, over and over until all my lines were zig-zags, and realized my value should have been my initial "2.5" instead of "67"
3)assuming your alignments are good, and your overspray is only horizontal, I'd check your encoder. I had similiar problem with my Jv3-160, where my new printhead was still giving me ghosting around images. solved by cleaning encoder strip...which lead me to checking the encoder sensor while I was at it. upon removing the sensor from the machine, I noticed a dusting of magenta pigment on the lens. Cleaned it gently, reinstalled, and had worked 100% again for another year until finally retiring the machine for an upgrade.
I chalked it up to dust/hair/whatever deflecting the light from the sensor and giving the machine inconsistent readings along the encoder strip... causing printheads to fire erradically.
