I've been feeling my 3.slow has been running a little off lately, like maybe 140 versus 150hp.. By accident as I was relocating my front diff breather I saw my plug wires were resting up against my egr tube.. methinks hmmmm egr gasses hot, not good... I pulled them away and saw a little burn spot on the wire. I replaced the bad wire with one off my old set and instanly the truck idled a little better and felt like I was getting full use of my 150 midget ponies.
The culprit was a loom piece that had cracked with age and was supposed to hold the wires close to the block. easily fixed with a zip tie!

 

Glad you found that!