I have a 2002 with the 5.9L that has as issue when it is cold. It seems to start and idle right but when I give it gas it hesitates and runs rough until it warms up, then it runs as normal. I have changed plugs, wires, and PCV valve with no change. Also seems happen more often when it is cooler and damp out, and when it is warmer out it does not do it at all. A few weeks ago I did have a high voltage error from the oxygen sensor after the cat, but I under stand this does not have anything to do with the running of the truck, only shows you if there is an issue with the cat. Is this correct? I reset the error and it has not returned. Any Ideas?

 

Check your cap and rotor..... possibly getting some moisture in there. If those are OK, check the TPS, make sure the voltage climb as you open the throttle is nice and smooth. (analog meter is best for checking these), if it hops around, replace it. (test when cold)

 

for hesitation - check for vacuum leak.