Easy fix, yes...once they found the root cause! Lots of labor hours to find was the hard part. Electrical issues are always the hardest to solve. John said the truck mechanically is in great shape. I have to say that John and his gang at SD Trux are truck magicians! They make every bit of the 60 mile each way trip to them worth it. The O2 sensor wiring harness connector in the engine bay had a little corrosion and was cross connecting to a heater core connector and thus getting excess voltage from the constant powered heater core connector causing probably both my frequent #1 O2 sensor burnouts and the code 26 rich signal. Connector replaced and I had them replace the spark plugs, oil, lube, etc. while it was down there and again, as usual for SD Trux, she's running as smoothly as the day I drove it off the lot in August, 1994.
THANK YOU John and SD Trux AGAIN!