Welcome to modded DSM's. Cooling is always fun with these cars when you have a big ol FMIC sitting in front of your radiator. Things to try:
1) Run an FMIC that has some decent flow through properties. An extremely dense external fin setup doesn't help air get to the radiator. When I changed from a dense Garrett core to a higher flowing ETS core, that made a large difference in my specific situation.
2) Stock fans are the best fans. If you can fit stock fans then run them. If you go aftermarket, make sure you get ones that have a shroud. Ziptied 12" fans on the radiator aren't ideal at all.
3) Make sure your cooling system is in tip top shape. New coolant, radiator is in good condition, no leaks, good thermostat (there are lower temp thermostats available), good rad cap (there are higher pressure caps available).
4) If possible, run a more ideal coolant mixture for cooling. 50/50 provides a nice balance of cooling, lubricating, and boil/freeze protection. If you up the water content to run say a 70/30 mix, popular belief is it will cool better. Consider adding something like Water Wetter to help break up some of the friction (some people have ran a couple drops of Dawn as a cheap alternative to WW).
5) Create some air ducting to try and route more air to the radiator since you're big old FMIC is blocking a lot of it now.
6) Consider an aftermarket radiator. They are often larger than the stock one so you've effectively increased your coolant capacity. Maybe just be a few ounces more capacity over stock, but every little bit helps.
7) Try different water pumps. There are a few different blade designs out there. Last I researched the topic, the two designs were "exposed blades" or "covered blades". The covered blades supposidely was a better design, less cavitation. This isn't a DSM pump, but just an example of what I mean when I say exposed or covered blades.
