Transmission or drive-train issue/low idle rpm

Hey guys. I just recently got myself a 4g94 2004 GDI pajero io (automatic 122,000 I’m) and have ran into various issues that I’m having difficulties troubleshooting. Firstly, thank you for reading this and I hope I can provide all the information that can help you guys troubleshoot this with me. 3 times in the past week and a half, the transmission has seemed to slip out while I was driving roughly 40km/hr and slowing down. All times this was within 5 minutes of getting the car moving and before the car has fully warmed up. It has made a squealing noise and hasn’t resolved until I have completely stopped the vehicle and resumed driving. Luckily this only happens when I’m on the side roads so I am able to stop or pull over and the problem has quickly resolved. The last time it happed (last night) I smelted a burning smell. I have already checked the ATF fluid and it’s red and doesn’t have any particles in it. Seems like it was flushed and changed in Japan prior to me getting it. I’m confused on whether the transmission is failing. The times it did happen, I was in a rush and live in a very hilly place and didn’t warm up the car as adequate as I should. What should be other things I need to look for? There is no oil leak and the levels of atf seem adequate. I also drove this car 70 km on the highway yesterday going 90 km/hr and seemed to not have any problems shifting gears. A weird additional component of this problem is when I’m going up a hill, it seems to struggle to switch gears and deactivate gdi eco (don’t know if this is a common problem). Timing belts and such have all been changed.
The second problem is low idle rpm where the car shutters when I’m in traffic. I changed the spark plugs and cleaned the throttle body but the problem persists. The problem isn’t bad all the time, and when the fan kicks in, the rpm’s resettle. This discovery has made me keep the ac on a majority of the time as this engages the fan more consistently and keeps the idle smooth. Think it could be the idle control valve or sensor, but how does the fan fit into this situation? I hope I get some of your expert opinions so I can keep my dream car running smooth.