I'm trying to put your advice to practice, but it's tough because I'm still very new to this.

I managed to get all the gears working perfectly except the lowest two on the small chain ring, which I'm okay with because I very, very rarely use such a low gear, and spend all my time on the hardest 4 or 5 gears typically.

Not completely sure what I did differently but it worked. I'm going to take down the alivio tomorrow and try some of the things everyone suggested some more. This is something I want to eventually understand inside and out. I've always been the dude with ****ty shifting on his bike and a clanky chain, because I had no idea how to adjust geared bikes. This is the first time I've managed to "fix" one this well. Only going uphill from here lol.

Fietsbob, if I have time tomorrow I'll stop it by a bike shop just so they can look it over and tell me what NOT to do next time