Two things that are common with those year dodge trucks to look for. First they are known for plenum gasket, under the intake, leaks. You can check this by using a vacuum gauge. Pull and plug the PVC hose to intake nipple and plug your gauge to the crank case hose end, where the crankcase vent usually attaches. Start the engine. You should only have a 1 or 2hg of positive pressure(if I remember correctly). This would confirm no plenum gasket issue. If it shows a significantly different reading, you have an issue. There is a nice video on YouTube about this. My next guess and likely your culprit is a gummed up/ carboned up IAC. They get dirty and this causes the throttle blade not to open and close properly causing the computer to try to compensate with adding fuel. This occurs at first start up when the truck is in closed loop or warm up mode as it has not gotten hot enough to start using input from the O2 sensors at that point and likely the reason it does not throw any codes. Clean or swap out the IAC motor. I think I paid $30 for mine. Took 15 mins to replace using a #25 torx bit on a small ratchet while intake was still on the car. Solved my problem, might solve yours too. Good luck.