Has anybody noticed a propane type smell comming from the A/C when hitting the brakes? I know it sound wierd, but it definitely happenes when I hit the brakes.

There must be a odor being generated by the front or rear pads that is somehow getting sucked into the vehical. Is it the same whether you break hard or easy?

Usually when braking hard. Going from maybe 45 to a red light.

It has to be brake pad related. If it is really bothersome try changing brake pads to non GM replacements.