jwramc's video: F350 erratic idle and stall issue Got a fix

My recently acquired '99 F350 5.4L 4x2 with 214k.mi. will start normally, and go to a fast idle warmup. Tach shows about 1300rpm. After 90seconds or so, the revs drop a bit... then again at 3:30mins... and there will be ups and downs over the next few minutes til at about 9:20 in the linked video, the idle drops VERY low, the engine 'lopes' a few times as if running on 2 cylinders and then stalls out completely. If you'd care to give it a listen for almost 10mins of video, follow the link. If you just want to hear the moment it does the huge drop and stall, jump to about 9:15 in the video. Temperature doesn't seem to matter, but on this occasion, the truck has sat unused for 48hrs. The night before the temp dropped to 12 degrees, and it's 11:45am and 18 degrees when the video begins. It's got a new fuel filter and has run through two tanks of fresh fuel since purchase a month ago. The recent tankful was treated to a dose of dry gas and injector cleaner to try and remedy the issue, but no change whatsoever has occurred. I figure before I start buying pricey bits or send it to a mechanic for a big-buck fix, maybe somebody can point out the best route to diagnose the issue... or even better, has a quick fix ready to go. Any thoughts?