Well, replaced the rad with a new one. Checked the presence of the baffle with a small stone and it didn't go through. Checked the temperature on the water intake, exit and at the bottom of the rad and it all looks good.
Unfortunately it is still overheating on big inclines and it seems to be getting hotter quicker. On the incline that I've been using as a test, this time I couldn't even make it to the gas station on the top
Engine temperature was reading 124ºC (!!!) and the gauge was in the red with the red light on. After letting it cool down and reaching the gas station I drove it there for a while and the temperature came back down to 85ºC and I drove back home (some 20km) without problems.
It seems that it is overheating only when it comes under severe load.
Any suggestions ?