AA 963 arrival 9:25 AM (I assume Terminal 3) DFW-GRU
G3 7600 departure 10:15 AM (I assume Terminal 2) GRU-VVI

International traveller with Hong Kong passport. Not checking in luggage. Two different tickets.

Questions 1:
Do I need to go through immigration?

Question 2:
If Q1 is negative, how am I going to go through customs?

Question 3:
Do I have enough time to make it?

No way. Sometimes there are delays in deplaning. You will need to go through immigration and customs. Even if you checked in online, I would put your chances of making it at 1 in 3. If you miss your flight, you will pretty much have to buy a brand new ticket.

If the ticket was cheap enough, you can keep it, while double-booking on a later flight and try to see if you can make it, and cancel the later unused flight.

Well, it depends if AA and G3 have an interline agreement that allows luggage to be checked across two PNRs.

That only happens if you have to collect your luggage.

Only if you don't have luggage or it is checked through. Download Gol's app and do the check-in process through it, since it is possible that you will be unable to connect without going through immigration if you don't have a boarding pass.

Thanks for all answers.

At least I want to know, terminal 3 and 2 doesn't matter in my case, right?

I am flying F to GRU. Hope it helps being the first passenger offload.

What I mean is, the departure gates of the three terminals are "shared", only the check in counters are in different terminals. Right?

No - everything is segregated. They are adjoining terminals (small walking distance), but boarding areas are completely separated, with no airside connection.

OP, you didn't say what day this was happening, so perhaps it is already past. If you are on G3 7600 to VVI, that is Bolivia and you would be making an international to international connection. In this case, you could stay airside and not go through Immigration and Customs. There are signs and usually agents that will direct you. Of course, you would need to BP for G3, and I am not certain where you would get that unless you can do so online. Today G3 7600 left from Terminal 2, Gate 239.

Finally I have decided to stay in GRU for 24 hours instead of transiting on the same date since I might have some check in luggages.

Thanks all

Wise decision ^

That is not true.

I'm similarly situated to the original poster. AA long-haul into GRU, premium cabin. Possible G3 onward flight (domestic within Brazil). I'd have 65 minutes (based on flight schedules). Separate tickets. No checked bags.

What should I expect for passport & customs at GRU for a US citizen at peak time on a weekday morning?

Could buy a refundable ticket on G3. Then it hurts less if I miss the connection.

Would certainly want to download Gol's app to do check-in that way, or print boarding pass before departure from US the night before. Any reason to think I wouldn't be able to do this?

Coming back, I'd have 85 minutes. In case of misconnect, I'd be on a flexible AA ticket so could change to a later flight with assistance of AA staff and pending inventory (which doesn't look like a problem).

Definitely not ideal. Odds seem ever so slightly better than the original poster, 65 minutes rather than 50, which is a big difference. Makes me pretty uncomfortable though.

I just made an EZE-GRU-JFK connection in less than 15 mins. Super easy, no immigration/customs needed. just a quick security check with no one in line. I was dumped right back out airside in T3, or was also given an option to stay airside in T2.

I think this connection is more than possible. I know MCT for I-I for for Oneworld is 60 mins. I had 55 mins scheduled layover time and i still made it thru to T3, to the LATAM lounge for a shower, some snacks, picked up some water/coco water and got back to my AA flight when they were calling boarding.

Just remember that coming in from EZE, your flight could have landed at a quiet time, whereas coming from the US on AA, it's almost guaranteed to arrive in the early morning crunch time. Having no baggage helps, as does checking in via the Gol app.

65 mins with no luggage AA-G3 should be quite doable, but I concur it's best to have a flexible ticket (in theory if your inbound AA flight is delayed you can take a later flight on the same day at no charge, but you can't make the change on the app, and only prior to flight closing).

bedelman also mentioned he was doing international to domestic, unlike yourself which was international to international.

Even with no checked bags, he will need to go thru passport control and then thru the customs area and duty free store. A GOL flight will likely leave from the far pier in Terminal 2 (the old Terminal 1) and that is a 15 minute walk plus going thru security. There is a recheck desk area after exiting the Customs area if the boarding pass has not already been obtained. Could been done if flight is on time and lines are not too long. Still risky. I prefer 3 hour connections.

65 minutes is doable if everything runs well, but I wouldn't rely on it.

Mandatory is that the online check in for the onward flight works. For JJ flights I had never issues doing that (72h in advance), for AD flights it usually didn't work. No experience with G3.
Immigration in most of the times runs quite well, as long as the flights are on time. Last time we had to wait 15min in front of the gate because it was still occupied. Meanwhile another flight came in, and the queue at immigration got naturally quite long.
The recheck desk area can bother you for 5 minutes or 30. Then walking to the other terminal and passing security, which domestic typically works pretty fast.

So overall it's possible, but I personally would aim for at least 90 minutes.