How much faster will my 0-60 be with 3:73 gears in 01 v6 firebird?

Depends on what the old gears were and how much power the engine can produce. Going from say 3.23 gears to 3.73 will theorectically lower the top speed and increase the power to the rear wheels for acceleration by about 15%. How much the change will actually be depends on too many factors. (traction, shifting, etc.)