two mornings ago I go out to start the truck and I all get is the click.

Battery volts was below 12, so I suspect the battery is discharged. Maybe I left the door open or something.

I jump start the truck, and check voltage. 14v at idle. So I suspect that alternator is ok. Battery is only 1.5 years old.

Drove for about 1 hour total, with a few stops and restarts. Dash guage was right in the middle. I figured this would charge the battery a bit. Always started with no signs of low battery.

Next morning, go to start, dead. Battery is at 10v!

So it looks as though I will need a new battery, but what about alt.? Here is the twist:
I have a autometer tachometer that runs off the alt. I noticed it stopped working completely about a few weeks ago. This makes me suspect a problem with the alt as well. I dont want to replace the battery and have it go dead again in a few weeks.
Is 14v at idle a sufficient test of the alt? Could it be putting out 14v but not enough amps?

 

have battery load tested before buying new one, sounds like something is draining batt overnight.

 

Or, your battery terminals are corroded isolating the battery from the alternator. 14V should be sufficient.

 

At idle, turn on a couple accessories like lights and blower, and check battery voltage like that. If alternator is doing its job, it should be able to maintain over 13.5 volts at idle while running some accessories.