I had a simular issue with NO heat. What it turned out to be was a control valve inside the truck for the heat/AC systemthat was not opening to allow the blower to blow threw the heater core. So I had no heat. Both heater core hoses where hot to the touch, so I knew the coolent was passing threw the heater core. Fixed the control valve and wow got heat now.

 

yea change the control valve and if that doesn't work then ur problem might be something i ran into check your oil is it milky if it is then u have got blow by in your intake manifold and you will have to replace your gaskets with felpro pinto gaskets. just wanted to cover all basis.

 

A friend of mine with a 96 had a problem like that after he flushed his cooling system. I think it had something to do with air in the lines. He said the system had to be bled. I mentioned that I planned to change the thermostat in my truck and he told me that I might have to do that when Im finished. Could you be having the same problem ??