95 chevrolet k1500 No heat at idle

I have some semblance of heat when im driving,
but when I let it idle, the heat turns cool.. Not cold
but cooler. I swapped the heater core a few years
back and bled it. When I let the truck idle up to
operating temp. I check the hoses and the hose
leading to the back of the block is hot but the hose
running to the water pump is not as hot, until it
gets closer to the water pump, the closer to the
water pump the hose gets, the hotter the hose is.