So this is my first diesel. 03 5.9l with 85k original miles.very clean. I went out this morning it was about 28 degrees and started it up no smoke starts right up and then when it idles it almost sounds like its missing and the lights dim a bit just for a split second then brighten back up. Doesn't do this constantly. Drives and runs smooth only smokes when I get on it to appease my three year old son. No cel and I'm getting 23 mpgs. Also I noticed that after driving on the highway for an hour after it was parked and idling in asking lot about two minutes it started to do the lights thing again and the engine sounds a little misfirery but its not a misfire. Any thoughts?

 

the lights dimming is your pre-heating system continuing to cycle. my 2004 sounds like it has a little skip as well when i start it cold and it goes into high idle. not sure the cause

 

That must be it. I could not find anything describing what I felt was the exact problem or issue I thought I was having. I bought the truck last week on a hot day and did not have this issue so it was just alarming.