Picked the truck up from the local shop today- guy didn't do much other than test drive it and said he thought it was the IP. I took it to the shop, changed the fuel filter (spin on on my truck) even though I just did it 1500mi ago, and poured a liberal amount of Diesel Kleen in the tank (and a capful in the new filter). Started her up and wow, idle way up and much smoother, quieter. Test drive revealed the problem still present, though, 1500 and 2000+ RPM bad vibration and hum. Thinking the rough idle and running and the vibration were 2 different problems, perhaps, and I may have half-solved one. I don't doubt the IP may need a rebuild, though- the tag stamped "E" that Chaski noted is not present on my pump.
Went trough a bunch of things and did notice the truck really doesn't want to shift into N or 4L on the transfer case. No problem between 2H and 4H but I've got to shift between D and P a number of times and keep trying the shift to 4L and eventually it'll go. Not sure if that indicates a related problem with the transfercase and the buzzing/humming vibration. I'll take a closer look tomorrow when there's light.