Did you do the follow when flushing the system??
This is from the Dakota service manual
3.9 V6
Draining system:
-Remove radiator Cap
-Loosen radiator draincock
-Remove cylinder drain block plugs
Refill system:
-Install cylinder drain block plugs
-Close radiator draincock
-Fill the coolant system with 50/50 mixture of water and antifreeze
-Fill coolant overflow tank to the FULL mark on the dipstick
-Start and operate engine until thermostat opens (upper radiator hose is warm to touch)
-If necessary add 50/50 water and antifreeze coolant to the overflow tank. This is done to maintain coolant level between FULL and ADD marks. The levels in the overflow tank may drop below the ADD mark after three or four warm-up and cool-down cycles.
Is the radiator full?? If so, the overflow tank levels will not move. Run the truck and keep an eye on the overflow tank for the next few days and see if the level moves.
Anthony