4900ex improve my cooling

I have a 2006 western star 4900ex. I am looking to improve my cooling. It tends to temp up on the longer pulls. Run inbetween 90,000 to 100,000 lbs loaded. I have good power, but have to slow way down to keep things cool, even with the fan on.
It has a c15 accert with an 18spd. The radiator has the upper radiator hose on the drivers side and the passenger side outlet is down low. It does not have the bolt on flange underneath, like my parts Star has. Cools ok when empty around 60,000, holds pressure with a tester. Oil cooler is separate.
What suppliers make a bigger or thicker radiator for my application. Thinking of changing it out when I do my thermostats
Has anyone had better cooling using that PDI oil cooler. Claims about 10 degrees drop in oil temp.