Tahoe brake problems

I have a 2000 Tahoe and last week I had to slam on my brakes. I ended up bumping the car in front of me, no damage. As the week has gone by I have noticed when I push on my brakes, at first they're hard and then they push almost to the floor. There is a hissing-air noise coming from around the pedal when I push on them. We have checked the brakes and pads and everything looks good. I know at one time there was recall, but my dealer said it's a VIN specific recall and it doesn't include ours. Any ideas would be great. Thanks

Sounds like your power brake booster is leaking.