valve ping?

[APOPKAROB]

2.5 dohc has valve ping after 55 in o.d. no codes is not fuel octane related still happened after timming belt swap won't go over 75mph and had to feather fuel to it to keep from pinging the valves. problem used to come and go and has got worse now happens most of the time. ANY SUGGESTIONS? would be nice as it's been a good truck.

 

[APOPKAROB]

I'd rather have no replies than a bunch of dumbass ones!!!!!!! FOR PARTS CHANGING TILL IT RUNS BETTER