I'll try to make this brief, new radiator, T/stat, fans working, pulled w/pump to be sure the impeller wasn't rusted off. I think it has an air pocked, but I have used evey method I know to fill the system. Will not over heat at idle. Ran in shop at 2k rpm for a while after reaching operating temp, still ok, drove for aprox one mile and overheated. This is a strange one.

 

Well if its an air pocket the easiest way to get it out is to elevate the front of the vehicle so that the front end is the highest point of the cooling system, meaning that the air will travel to the highest point. Did you make sure that the propeller on the water pump was still fixed to the front pulley and not slipping at all?