Heat Problem

My '87 4.0 pumps out luke-warm heat from below the dash. However, if I set it so the heat comes out the dash vents, it seems to be hotter. It runs at a constant 190 degrees, there doesn't seem to be a heater-core leak, and the blower works fine. Any thoughts?

try removing the hoses from the heater core and back flushing the heater core and see what happens, it may be stopped up.