Took the Barracuda to the track today for first time
From what it sounds like it just didn't have the stones to keep accelerating in high gear, which tells me cranking compression is really low.
If it was fuel delivery, it would stutter and miss in high gear, which he says it didn't. Hurt valve springs would show itself in the burnout box as well as high gear.
If it was mine, I would do a cranking compression check. If they all show low, drop down to a .484 cam or one of the 340 grinds, and possibly swap to a thin gasket or even get the heads cut .050. Even a low compression 360 can be deep in the 12s with the right pieces...