Lately, my 2004 Suburban 1500 2wd has had the voltage gage pegged past the 19 volt mark. Truck starts and runs fine. What's the best way to start troubleshooting this problem?

 

Put your meter on battery and see what it is actually recharging at. Could be a cluster problem. A shop would be able to diagnose this very quickly for you. They can see what the actual voltage reading is being sent back to the IPC is and can perform a sweep test of gauges.