The Heater core is difficult to replace on the RAM since it is buried in the plenum box. The box has a convenient door panel that you can open to remove and replace the core. The catch is that the convenient door is on the back of the box and you have to remove the heater box to get to it. This involves removing the steering wheel, steering column, complete dash panel, evacuating the AC, draining the radiator, and finally removing the heater box. Once you have the box out(8-12hrs), the core is simple to replace. You want to be sure that the core is the problem before you undertake this process. If there is a strong smell of antifreeze in the cab or a puddle of coolant on the passenger side floor, the diagnosis is easy. Check that the radiator is full, not the overflow tank, the radiator. On a cold engine you can remove the radiator cap and check the level. It should be full. If there is air in the system it will affect cab heating and engine cooling. Another good check is to feel the two heater hoses going into the firewall from a cold start. The hoses should warm up at about the same rate and get uncomfortably hot-close to radiator temperature. If the core appears to be OK, the next concern is with the blend doors that divert air through the heater core. This is a common failure on the RAM. Check heatertreater.net for an explanation of the operation of the system and a fix for the common problems. The RAM has four different DC servo motor controlled air flow doors that are susceptible to failure and all of these need to be checked by either observing the symptoms of failure or reading the codes. The problems are easy to fix with the HeaterTreater kits, but the OEM dealer fix requires removing the plenum box as described above. It is a costly repair if you take it back to the dealer and are not under warranty.