GRU is a nightmare and it's getting worse and worse. Allow yourself plenty of time to check in and to travel from GRU to town.
Last Thursday, it took me two hours to travel from GRU to downtown Sao Paulo. And on Friday, I was in line for 45 minutes to get through security and immigration in T2.
Sao Paulo and/or Brazil authorities need to do something to fix this situation. Business people, especially from those outside Brazil, will not put up with this inefficiency.