i had a similar problem with my 97 ram 1500 5.2L V8, roughyl around 140,000 miles, the weather wasnt as cold but my rpm would drop greatly when just idling in drive. The reason for this was that i had a blwon piston ring which caused an irregular action by the pistons causing the rpms to drop too low causing the engine to die. so that might be whats wrong but im not truly sure.

 

blown ring? dang dude... first ive ever heard a magnum having ring problems..


any results on testing your idle problem? another thing i was thinking is that check all your breather tubes...might be a long shot but if a breather isnt hooked up correctly or is cracked it may cuase something in your case... again i say its a long shot ...