95 Z28 Pinging

My 95 Z, 58k miles is pinging on acceleration when going up a grade on the freeway, especially when a/c is on and/or when I am carrying a passenger and
on warm days 85+ degrees.
The pinging was reduced considerably after a recent oil change, however when I took it in to the dealer shop, they put it on the computer, everything was perfect they told me. They test drove it after the oil change and it did not ping for them, same 'ol story. They told me if it happens again to bring it right in for a test drive.
I asked them to check the knock sensor, but has they said the computer did not show anything wrong, everthing was up to spec.
Any ideas?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Check to see if the car is heating up beyond its normal temp. Switch to synthetic oil to reduce friction and some heat. Run some cleaner through the fuel system.
Charles 1992 RS 25th Anniversary

and
when
was
not
it
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Where do you get 92 octane R+M/2? I'm been using premium 91 octane, thats all I can find here in the SF Bay area.

the
passenger
everything
did
bring
did
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

93 in South Florida, dude. It's everywhere... -- lab~rat >:-) Do you want polite or do you want sincere?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.