Did you ever find out the issue? Dealing with the exact issue on my 2020 Chevy custom 4.3l v6

 

@Flytrisk you're replying to a 12 year old post about 21 year old truck. I don't think they'll answer you. You'll get much better response by creating your own thread in the 2019+ pickup section, and describing the troubleshooting you've tried , please.

 

Check for lose plug wires. My #3 and #6 are always working lose, especially under load. My engine mounts are solid.