340 Help. Am I looking in the right spot to fix the issue

Did anybody check to see if the TQ was getting to WOT? Secondaries not opening?
Sec main jets? Some had small 0.125" jets; some came with 0.143" jets. Carb getting enough fuel? Air valve linkage operating freely?
Agree with RRR, could be soft valve springs.
Crane ground 5* of advance into most of their cams, & this cam has that. Doubt that this is a cam adv/ret issue.