Noticed today the voltage guage was around 16 17 volts. Any common problems cause this? Truck is 4.8 stock 104k miles.

 

Regulator in the alt could be going.

 

What's a typical voltage? Mine at idle is just a hair above 14V, and 15.5 above idle. I just swapped in a 145A alternator. This is using the volt gauge on the dash, is there a better way to read the voltage?

 

factory voltmeters are not to be trusted for accuracy. this goes for all makes and models, they give you a good idea if your charging or not but that's about it, not to used for any real diagnostics. get a handheld voltmeter or multimeter and test the voltage at the battery or between your positive power block and a good ground point, voltage on a healthy battery at idle without any serious draws on it should be 14.4 give or take a little bit...