I don't know what's going on with the heat in this truck. I changed the heater core filled it up let it run the heat blew hotter hell. The truck sat for a few days then I took a 25 minute drive and the heat stopped half way to where I was going. I thought it was my thermostat so I replaced that, again the heat worked great for about a day and now it's back to blowing cold air.

I am open to all suggestions.

 

Make sure the cooling system is full. Check the heater hoses to see how hot they are.

 

You could also have air in the system.