O2 sensors or vacuum leak?

I just took my car to get it fixed and they
replaced a vacuum hose, filters, and put a
new computer in. They said it should fix the
problem of it stalling when stopped at a red
light. It didn't. My car still idled high
occasionally and stalled when stopped at a
red light and then today started to give of a
hissing sound when accelerating and revved
really high before switching gears. Would
that still be the o2 sensor or is there also a
vacuum leak somewhere now?