It is always very difficult to debug a printer remotely, but here's my best shot. I may be totally wrong though!
Zooming-in your picture seems to show like little bumps (inwards or outwards) that offset the extrusion in the XY plane.
The fact the bumps occur on both the X and Y axis, and both inwards and outwards, and that the patterns are not fully regular make me think the problem could be as simple as the new printing head having some play, and some combination of forces waking bumping it momentarily off its intended position.
Any ideas or suggestions as to what to check next?
Check for play.
Play which is due to a static feature (like a loose bolt, a clamp not holding firmly enugh or a cracked heat break) can be usually be detected with the printer switched off, by holding the nozzle between your fingers and shacking it gently.
Play that is dynamic in nature (for example a roller with an irregular diameter or screwed parts becoming loose only when hot) can be more tricky to detect. The procedure is the same, but tou may have to heat the extruder (and use gloves, doh!) or to repeat it at different positions on the X and Y axis.