Thanks for all the advises. I had probably the most horrible day since I am flying lets start from the beginning: my original route was: EZE-GIG (on PZ 725, on a seperate booking), GIG-GRU (on JJ 3571) and GRU-DFW (on AA 962).

Arrived at the airport in EZE and saw that PZ 725 had a tiny little 4h15 delay, which would let us arrive in GIG at 4:55PM instead of 12:40, while our connection on the seperate ticket was at 18:35. So the agent in EZE was so nice to check our luggage through, but in the last second, I realised that our original problem, the seats on the AA962, have been changed. Realising that, I told her to uncheck our luggage again and I tried to call AA to rebook us from GRU via MIA for getting the Lie-Flats. After 1.5 hours on the phone, I got us rebooked to AA930 and AA61 via MIA, rechecked the luggage and got all the boarding passes until DFW. Everything seemed to be fine...

Well, until JJ realised, that they had no crew for their already delayed by more than 4 hours flight to GIG, which added another hour delay. So we knew that our connection in GIG will almost be impossible (new planned arrival time: 5:50, departure 6:35, incl. rechecking the bags and going through customs).

We were running like hell in GIG but, as expected, no chance to recheck the bag at 6:15, 20mins before departure of our JJ3571 to GRU. The JJ agent was not willing to help us, referring to our two seperate tickets, saying that we will loose all the remaining flights on the latter one. Having onward flights from DFW to LHR and ZRH on the other ticket, this was indeed a shocking moment for us...

So we tried our luck at the AA check in desk, and they were veryvery helpful, rebooked us to AA904 (old seats, but that was not our biggest concern anymore) and then to AA2305 (lie flat). Very nice gesture by AA and even though AA2305 was switched to an angle flat 767 some hours before the flight, we are more than happy to have finally arrived to Texas. Sorry for the long story, but I think I lost some years of living yesterday because of the stress...