2000 Dodge Ram missing real bad when cold but doesnt when w

I have a 2000 dodge ram 1500 5.2 liter v8 I recently changed out the wires and plugs and the distrbutor cap and rotor. I checked the gap on the plugs and have the wires all on the right cylinders. The problem is when the engine is cold it kind of bucks a little like it is missing and the tach flucuates just a little like it is being rev. Up and down. So then when the engine gets warm you can hardly tell that it does this at start up. I have investigated some possibilities with this and think maybe it is the Idle air control valve or the oxygen sensor. There are no lights on or faults coming up. Also the oil pressure seems to flucuate also once the engine has warmed up. It goes up and down as I accelerate and decelerate.