I've had problems with it skipping since I finished it.
There is always the possibility this is because the ink that comes in the cartridges with kits is nasty cheap stuff that has gone bad. You don't say what ink is in the pen - if it's a quality brand from a bottle, chances are it isn't what's causing the problem. Try Waterman's, Pelikan 4001, Parker Quink, Diamine, Pilot, ... there are lots of good inks out there - one of these using a cartridge converter will give a much better indication if the nib & feed require tuning.
Another possibilty is some gunk (technical term) in the feed channels. Get an ear/nose bulb syringe like
THIS and use it to force lukewarm water through the nib unit. A drop of ammonia in the water can help but isn't usually necessary. There are products called "pen flush" which are basically water with a tiny amount of detergent and ammonia, they do a good job dissolving any dried-up ink inside the nib unit without having to get the nib and feed out.
If you can get the nib and feed out of the section, use lukewarm water with dish detergent and a soft toothbrush to clean the channels in the feed. Then rinse off with clean water, reassemble and try again.
Tuning nibs isn't difficult, it just takes a little learning and practice. Richard Binder is one of the best, and his tutorial is a great guide. I have not yet had a nib which I couldn't improve using his methods.
One last point to consider: you've written multiple times that you don't think it makes sense to put a $20 nib on a kit pen that cost less than that. A fountain pen has two functions: one is to look & feel good in the hand, the other is to write beautifully. It's our job as pen makers to bring both of those to the highest level we can, and if the nib that came in the kit is junk, replace it with one that isn't. Doesn't have to be solid 14K or 18K gold, but it does have to write smoothly or we have no business selling it as a pen, it's just a pretty stick.