Issues dropping to a higher gear are almost always the result of cable friction. Sometimes a worn jockey wheel may be sloppy and you end up biasing the RD inward for decent downshifts, which, of course, means sluggish upshifts.

Two diagnostic tests I use to pinpoint the problem are as follows:

1- downshift to the low side of center, then carefully upshift 1 gear. If it hangs, pluck the bare wire from the frame like a guitar string, and if that completes the shift, and corrects trim, it indicates that the problem may be upstream, ie. HB to frame housing, or a sticky lever action. This isn't 100% reliable, but if you repeat the test and it's fairly consistent, you can be pretty assured that it's not the RD.

2- if the pluck test doesn't change anything, you can check for a sloppy pulley, either by winding a pipe cleaner or similar around the sides to reduce float, or even putting a non floating pulley there. Often it'll shift more cleanly without pulley float, but trim is more delicate. However, if reducing float helps, buy a new jockey wheel.

BTW- don't let the fact that yo put in new cables steer you away from cable friction as the cause. Poor alignment of the rear loop, badly cut ends, ferrule issues, and other factors can make even brane new and look right cables run slow which will mess up the upshift.