I resolved the issues a few days after the last post, and have been happily driving this vehicle.
This changed 1-9-2015.
Due to COLD weather, it has been running/idling 5 days = not turned off.
Preparing Leave work 1-9-2015, the idle was rough / stumbling.
I shut down for quick (safety) fluid checks:
#1. The engine temp was 75° C.
#2. Removed the radiator cap, no heat waves / steam.
#3. The radiator cap rubber seal (inside the radiator tank) had heavy frost.
#4. The engine oil level was a pint low, ignored = oil change next week.
#5. The washer fluid was semi frozen slush, added rubbing alcohol.
#6. Inspected the alternator / water pump drive belt = GOOD.
It re-started OK.
The idle was still rough.
Took off for work, throttle response was bad/poor as if it was a total COLD start.
I struggled to reach / maintain 65 MPH on the drive to work.
The power seemed to reduce further as I neared work.
(I know older forum members are chuckling, as you know what happened).
I stopped at the fuel station in front of work, and added two quarts of kerosene to the fuel tank.
By lunch time, the ambient temperature had dropped another 9° F, the engine temp was 75° C, and the car was happily clattering.
The idle was perfect, and all power was back.
The cause of this annoyance = fuel waxing.
Diesel fuel is prone to waxing or gelling in cold weather
.