My 2000 dakota and durango both have no cap on the radiator, just the cap in the hose. I would suspect you must have an early 2000 truck or something, I would use the 2000 radiator and shroud and you will not have a problem. I am one of the guys who pulls the mechanical fan out and I tow with both my rigs and never overheat either, even going up big mountain passes towing way more than I am supposed to. A stock 2000 set up will cool your 408 with no problem.