The phone will only report a 3G connection because that's all T-Mobile has is a 3G network. 4G is just a marketing tool because the HSPA+ network is fast.
If you discovered a virus I highly doubt it's in the ROM itself. I ran this ROM for a VERY long time with no problems logging into anything.
If you're trying to add a student email to the email app then maybe the schools service doesn't support Android. If it's just a website then maybe you should try an alternate browser and see if you get different results.
But more information about what type of student account that is would help.