Overheating issue

I am having an overheating issue on a 2000 RD 690

The water pump went about a month ago.  We change the pump, fan clutch, thermostat

Everything good.  Few days later, overheating.

changed all sensors on the manifold and all sensors for gauges-

Good for a few days-then again overheating

We flushed the intercooler and radiator.  Not losing any antifreeze in the head.  Took to 1 mechanic said it was the head

took to Mack dealer they are not sure, they said maybe internal. 

Maybe when the pump went something went inside   Any input on this greatly appreciated.