So I have a 2000 1500 5.9 and I was sitting at a light and went to go take off truck stalled out then took awhile to start had to push gas peddle and turn the key to get it too start. Had my battery gauge jump to 18v that same day. Now the truck won’t even turn over any ideas on what’s going on

 

Have you try turning the engine by hand with a breaker bar and socket? If the engine spins with the breaker bar. I would check the battery and cables next and also check how much voltage getting to the starter and check the ignition wire at the starter too.