1995 Ford E350 RV 460 Pre-detonation Problem

The truck has 15000 miles on it and has been thru 3 engines due to pre-detonation. Timing is correct but jumps around a bit, have verified
chain to be OK. has new distributer and pickup, ICM checks OK, Ive been
thru idle air , map & 02 sensors , any ideas what else could cause this
condition besides fuel quality???
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.