Update.
Scanned and cleared the trouble code P0336 (crank position sensor range or performance problem) on the truck. Started and test drove with no repeat of check engine light. Let it go and see what happens? Do codes pop up with out real cause once in a while?
Tach and charging system seem to be working ok.
Cheeers

 

I would say drive it and see what happens. It could have been caused by something as simple as a wet plug.
Tom