Should I Just Leave My Job?

Long story, but the biggest part is the last 2 paragraphs.

Ok, so earlier this year my job (just a local sandwich restaurant) switched owners. The new owner is fine, trying to fix things and that's all great. However, he's kind of annoying once in a while. I can understand that trying to prepare food according to the charts is ideal, but he basically stopped food production one day for 5 minutes (average to make 1-3 sandwiches in that whole time) to give someone a tablespoon so that they would put the correct amount of olives on a sandwich, and in the same day said that there was too much mustard on a sandwich when the person wanted extra mustard and he didn't check, and other little things like that. I don't have any big problems with the owner - it's the GM and another manager that I have the issues with.

The GM is basically rude to everyone on a regular basis, doesn't really work while she's managing (which the owner is 'okay' with) - she tells other people to do work and then gets on facebook or starts flipping through a magazine, which really makes me mad. Then for half the day all she does is take orders and take the food out to people - avoiding making food then bugging everyone about the time it takes for a single drive-thru order to get done while we're backed up in the kitchen and she just stands there and watches.

The other manager basically acts like I'm an idiot and don't know what I'm doing ever (and I've been working there 3x as long as her) - I'm essentially an assistant manager and I make some of the prep charts for bread that needs to be baked and I made one one night when she was there, then she turned around and told me I was doing everything wrong, half explained it, messed up the chart (which I ended up spending another half hour on when I needed to be out in the kitchen), then I came back later and found the entire chart blacked out and a note for the baker to just ask the manager for that day about the chart. I have no problems when I make the charts and I haven't had a complaint about how I do the bread charts at all about anyone running out of bread even when we're low on something (unless the baker is late getting to work, which, honestly, is not my fault), while I run out of bread I need on my shifts from charts that she's made herself.

The main issue I have is that I've been working there for 3.5 years and all summer I've been getting less hours than people who've been working there less than 1/3 the time I've been there - I'm fast in the kitchen, I'm nice when I help customers. I don't think I do anything wrong and I try not to. When I ask the GM for more hours, she'd just say that she could give me less hours instead while I'm sitting on 20hrs a week and someone she just hired is getting almost double that.

Some of the people I've talked to about it have said that I've been there for a long time and that it's time for a change, but I don't want to quit without having another job lined up. I applied at GameStop and I'm hoping they call me back - most of the employees at both the stores in town know my face bc I go there a lot (although I stopped bc money got tighter recently..), and one employee even said that she enjoyed my company, so I put her name down as a reference (was that okay?) on my application. They are hiring right now - everyone is - they're all losing workers going back to school. (I'm hoping he calls me tomorrow since he said either yesterday or tomorrow)

However if I don't get the job at GameStop I could probably get a job at the college I'm going to, and maybe even something that has to do with my major since I am in the final stages of it (just need 5 more classes to graduate). So should I quit even if I don't get the job at GameStop? It would be ideal since I've talked to a lot of the people there and I love videogames, but I don't know if I'll stand out against all the other people who applied (they had an open interview thing 4 days ago I missed due to work).

Should I wait until I have another job lined up before quitting? I have some money saved up so I could last for a little while, but I would need a job before too long since my major requires me to pay quite a bit to print off my projects and samples (art major of course..). School is starting next week so I don't want to wait too long since I won't have much time between the two jobs (I'd like to at least give 2 week notice; we're losing a few people too and I would feel bad just walking out right away) and school.