1994 Chevy Astro Heater

The heater only blows lukewarm air. The system was flushed and I replaced the thermostat with a 195 degree OEM. No improvement. The two hoses going to the water control valve are hot and the lower short hose from the valve to the heater core is hot. However, the upper short hose is barely warm. By the way the coolant that was flushed was suprising clean. I try to change it every year or so. This change in air temperature happened rather suddenly. It normally blows like a furnace.
Thanks,
Bob