There are a number of things that could cause this problem. I recommend performing some relatively simple checks:
*PCV valve - A sticking PCV will cause this problem, and will be especially noticeable in colder weather. If the PCV valve plunger sticks in the closed position, the manifold air flow is effectively reduced. This has the same effect as closing the throttle plate, hence, the engine essentially stalls. In colder weather moisture build up in the motor oil will gravitate to the PCV. In freezing temperatures the moisture around the PCV valve plunger solidifies and cuts off air flow. Look for any signs of moisture in the oil and change it out if necessary.
On a vehicle that old and mileage, I would also suggest checking the vacuum hose that goes to the PCV valve. I've seen these get gummed up to the point they no longer flow much vacuum.
*Vacuum hoses - Vehicles of this age typically by now have dry, brittle, and cracked vacuum hoses and causing leaks. This may not show up much at higher RPMS or road speeds...although it usually causes slight hesitation or surging...but will definitely cause idling problems.
*Sticking Idle Speed Motor - On Throttlebody equiped vehicles, the idle speed is regulated by the Powertrain Control Module (PCM) based on various inputs (sensors) in the system. The PCM then modulates the Idle Speed Motor to open a plunger-type valve that allows more or less air into the manifold to adjust the idle speed. This area is prone to carbon and gum deposits, especially with cheaper fuels. The Idle Speed Motor should be checked and cleaned, especially if you've never done is on this truck before. The Idle Speed Motor is easily removed on Dodge truck motors.
*Throttle Position Sensor (TPS) - This is essentially a non-linear potentiometer and can cause idling problems if the voltage is interupted across the terminals. This is caused by a corroded or dirty contact in the sensor. You can check this with a volt-ohm meter, preferably an analog type, by measuring DC resistance across the tap (slider) contact and rotating the TPS shaft. Erratic meter movement indicates a dirty or scratchy resistor. However, because of the miles, I would just change it.
*General engine tune - Of course, things like worn spark plugs, old spark plug wires, carbon tracked distributor cap and rotor, clogged air filter, will have a deleterious effect on engine performance and idle quality that may not have been noticeable in the warmer weather.
Good luck.
