Hey Scotty, 

I have a 1999 Chevy Silverado with 347,500 miles on it. It has the 5.3L V8 in it. For a couple months now, I have noticed a high idle after the engine warms up and has been ran for a while. It did not do it every time I used the vehicle, but 1/3 of the time, I had the issue pop up, no CEL codes.

Fast forward to last Saturday (2/18), I drove the truck about 35 miles to work, I got to the gate at work and came to a stop, the engine started running rough, like it was shuttering, for about 3 seconds and then smoothed out after I inched forward. It ran fine the rest of the day. 

Today (2/20), I was sitting in the drive thru at culvers with the engine off, but warm. I started my truck and it revved a little high on start up, the proceeded to run rough for, again, about 3 seconds. I put it in gear and inched forward and it smoothed out again and has ran fine since. 

What could be causing these random and short rough/shuttering moments? Could the high idle be related too? I would think that they are but I'm not an expert. The truck runs really great overall outside of a few small things, so I'm really perplexed with this issue. Thanks Scotty or whoever else answers!