I have allways used High Test gass 93 octane.
When hte car fist pinged serveral years earler the mechanic told me they changed the egr valve and it was fine for a couple of years.
The last time the ping started again took the car to the shop and the mechanic said the egr valve was leaking and replaced it again. Ping went a way for another year or two. Now it is back again.
A tec I talked to personaly said retail egr vales are not very good.
That I need to get an egr valve from GM. I did that but have not put it on yet. I hate to bring the car to caddilac because they wont to charge
over $500.00 to do a tuneup. Just to fix the ping.