overheating

I have a 1998 Caddy sedan Deville D'elegance 4.6 northstar with 165k miles. It has an overheating problem. My radiator popped and I replaced it. The engine still ran hot. Changed the water pump, thermostat, and hoses. I also flushed the system no blockage or air. The main problem is that there is no circulation in the cooling system once you go over 50 mph. The lower hose stays cold and the rest get hot. There are no signs of a blown head gasket, no white smoke no oil and water mixed, nothing I am pulling my hair out. I've lost my job, money and time (2 weeks) trying to figure this out. Please help.