2001 Dodge Ram no heat

I have a 2001 dodge ram with a 5.9l. When truck is driven until temp has com up to around 200, I have very little heat and if you put your hand on the radiator, left side has a small amount of heat in it and right side is cold. Upper hose and heater core hoses are hot, lower hose is cold. Water pump and thermostat have been replaced, (reman pump). I have tryed a known good radiator with same results. I also flushed engine with water when I replaced pump. Any ideas on why there is no heat in my radiator