Sounds like the work you did on the manifold is paying off……. Nice job.
On a low deck 452 I tested years ago, a basically ootb TR lost 37hp from its peak at 6200, to 6800.
Then another 76hp by 7300.
It had all the classic signs of a valve train control issue……other than it sounded fine.
I would have probably explored that some, but I’d already made a bunch of pulls with a single plane and a dominator, and it had a very nice curve up top with that combo on it(lost 27hp from its peak at 6500 up to 7300).
The TR lost 113hp from its peak at 6200 to the end of the pull at 7300.
Peak to peak the TR was up 20tq/26Hp to the single plane………but at 7300 the single plane was up 60hp.
Some formula I found at the time showed the TR to be tuned for about 6000rpm on that combo, which seemed pretty close.