On water heaters that have both fittings on the top, the dip tube is part of the cold fitting, it directs incoming cold water to the bottom of the tank when hot water is drawn off the top.
I'd check the thermostats.
IIRC, the top element heats until the water in the top half of the heater gets to temperature, then the thermostat throws control to the lower thermostat, which heats the lower water until it reaches temperature, then opens.
