You have two heater grids, one on top of the other. It will start hard & blow blue smoke if one or both are not coming on when it's cold. Usually it's one of the relays bolted to the driver's fender well. Don't depend on the volt meter fluctuation, the meter will behave the same with only one grid heating. Check to see if BOTH grids are getting current. Relays are easy to replace as a set but the Dodge dealer is the only place I could find them.