1997 Ford F-250 heater trouble

My Heater is not getting hot. I have checked the hoses - they are hot. I flushed the heater core. I opened the cover to the heater core. Heater core is hot. Blend door is functioning properly. fan is working. Hot air blows out of the exit side of the heater core. When I put the cover back on I get lukewarm air out of the vents. Same on floor, vent and defrost. It seems that either the heater core is suppose to be way hotter than I think is normal or somehow I am getting cold air in my vents mixing with my heat.

Te blend door shaft itself may have split.

There’s three parts to do a proper repair.

Tester