Hi cb, you have either a problem with the heater core or with your temp control door. Get the truck hot and go under the hood. Locate the 2 black heater hoses which go into the passenger compartment . These hoses should be so hot that you cannot leave your hand on them. If they are NOT hot,then you do not have hot coolant flowing through the heater core. Be sure the coolant is COMPLETELY filled in the coolant overflow plastic bottle.If the system is full and those hoses are not very hot,then the heater core is partially clogged. You can try to flush it out. Let the truck cool down and remove both hoses from the heater core under the hood. You must now flush those 2 metal "tubes" with a garden hose trying to remove debris from inside the heater core. You may have to rig a 5/8 " piece of heater hose onto the heater core tube and then to the hose to gain access. Try to get as much pressure as you can into there.When done,do the second tube with the same procedure.
If the hoses were hot when checked then the core IS getting sufficient flow and the door under the dash is not moving to the full "HOT" position. If this is the case let me know and I will try to walk you through a fix for this condition,however, this is more rare.
Good Luck and let me know how you make out.
yes, if you are sure the system is full and the truck is not overheating,then you have a clogged or partially clogged heater core. Follow my directions above and try to flush and reverse flush the core. Hopefully you can clear it. Remember the coolant should be replaced every 3 years or 30,000 miles. If that hasn't been done, this could have helped cause that problem. Anyway, try to flush that core. If it cannot be flushed then it needs to be replaced which is a MAJOR job. This job would take a professional technician about 8 hours as the entire dash and HVAC box must be removed. Good Luck. Please click the ACCEPT button if I have answered your question. If not let me know what else I can do to answer the question.