Hotter heater possible?

I had the same problem with my Dakota. The problem was the heater core is stopped up with gunk from not flushing the coolant on a regular basis. What I did was back flushed the heater core. What you do is pour water into one heater hose and blow shop air through but opposite of normal flow. Make sure you place the other hose into a antifreeze jug to catch the gunk in the heater core. You may have to do this several times until the water is clean. One way to make sure you have a stoppage is to feel both heater hoses at the heater core under the hood. The temperature should be about the same. If not, now you know.