2004.4 Rough Idle problem

I'm more of a lurker on here than anything else, however I could use some advice on a problem I'm having with my early 04 5.9 48re dodge. Backstory: Purchased new in Nov. 03, oil religiously changed at 7500, fuel filter every 15,000, engine has NEVER been touched aside from an alternator, fuel and oil filters. Recently I noticed what seemed like a miss at idle, feels like a vibration that I was not used to so immediately I was concerned. With my Modis hooked up, at idle RP was in thr 6kish area and at WOT it peaked at 25kpsi. This is with a smarty jr turned all the way up. No check engine light, no codes, no leaks and the truck runs fine at anything but idle. Did a WOT run to 110 and it felt great. Decided to add some Diesel Kleen to full tank of fuel and put a tank through it. Got 100 miles out of a 1/4 tank of fuel...seemed a little low to me compared to normal. On average I go 450-470 miles on 27-30 gallons of fuel. Typically 16mpg or somewhere in that area. No white smoke, no abnormal smoke, truck is NOT making oil and sits perfectly level every time I check the stick. Any thoughts as to what this could be? I did an injector shutdown test via my MODIS and #6 injector (cylinder 4 IIRC) seemed to make very little difference whether it is off or on. The other 5 had a noticeably poor idle quality when disabled one at a time. Truck has 191k on it and everything under hood is original...valve cover has never been off. I am about to condemn injectors...thoughts?