A quick check with a laser temp gun would tell you all you need to know. Check the temp bellow your thermostat, and above. Check temps between the cylinders on the block for hot spots, and at the heads. If you think you may have an air pocket trapped in the heads, elevate the front end as high as you can then pressurize the system with a pressure tester. This will coax the air out of the back of the heads. With your new aluminum radiator, the heat transfer should be pretty good. Thermostats have been known to be faulty out of the box, (especially CAT thermostats as of late), so that could be a possibility, but I am leaning to the air pocket. On the C-7 CAT diesels, we have to pressure fill them from the bottom up, or you'll be guaranteed that you'll have an overheat condition from trapped air. This is caused by the configuration of the power pack assembly, and the radiator positioned on top of the transmission. Too many bends and hoses with tight radiuses.