My .02 would be……..
With 140/375 spring loads, unless that cam had pretty aggressive ramps………53-5400 would be a pretty low point for there to be any type of lofting or valve bounce going on.
That’s not to say it couldn’t have been happening, but at that rpm, I’d consider it an anomaly.
However……….it does show up fairly regularly at a point not much higher than that(57-5800).

That dyno must be at a fairly high elevation……….the correction is quite high.

Also, I’ve had several sets of TF heads here with that 16094 spring, which is a PAC 1294.
TF has different specs for that spring depending on what documentation you’re looking at.

On my spring tester they check the same as the PAC specs, and the TF specs in their valve spring listings.
Those specs are stiffer than the specs that are on the instruction sheet that comes with the heads.

The PAC specs are 154@1.950/431@1.300……428lbs/in