With a large core FMIC, you need to get creative with some ducting to get more cool air to the radiator.
When I installed my E316G, the J-pipe didn't clear the fan on the drivers side and I had to remove it. I had issues when the car wasn't moving enough for air to flow through the radiator and had to shut the car off at stoplights to keep from over heating. When it was a REALLY hot day, there was nothing I could do to keep it cool even when highway driving and had to leave the heat cranked.
I installed a SPAL fan wired to run all the time to pull air through which helped a ton. You could also get another mounted on the front of the radiator wired to push air if the additional pull fan is not enough.
Good luck! Large FMIC's always cause this.