I looked at TAM's site, there is absolutely no indication about which terminal they use now at GRU, is it wholly T3 or T1 domestic, T3 international...
The latest news there are from 17 April
IME, there is a free bus (landside) connecting the terminals (I had to go from T1 to T4). It takes about 10 minutes, plus 10 minutes wait. I suppose with T3 will be something similar.