Thanks to all the folks who responded.
It must have been a bad tank of gas. ( ??? )
Fortunately, I didn't rush to the GM dealer.
I poured a container of "Injector Cleaner"
in the gas tank and took a 150 mile Interstate trip.
Seems to have done the trick. Engine is back to idling just as smooth as ever.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.