2003 Tahoe Service Brake Booster?

[hack27e]

I have a 2003 Chevy Tahoe 2wd 5.3 LS. For a week now the service brake booster message has been showing on the dash. The brake feel really bad as well. They feel almost hard when pressing the pedal. There is also a humming or hissing sound that will show up when applying the brakes.

Not sure if this is related, but there is also an oil leak and the AC went out. I read somewhere that a vacuum leak will cause all three of these.

Thanks!