Wow! The OP has already has received good advice from his performance shop as well as here on Stangnet, now he just needs to gets out to his garage and gets to work.Words to live by ed.
My curiosity got the better of me and I shot an email to the dyno shop in question, I just had to know what he knew or more accurate, what he saw on the screen, he told me he remembered the session and like the car owner was disappointed in the results, he said he suspected 'an internal engine' problem. Advancing the timing made no improvement. The a/f was good. He made no recomendation as to what was amiss because he was not involved in the build but timing issues were suspected.
The reference to the F cam was mearly an example of how easy it was to make 300 hp with the 5.0 h/c/i and supporting tb and LT headers in the past.
Travis needs to go back and degree the cam, check his valve adjustments and make sure he has no vacuum leaks.
And check for codes. A hot compression test and a leakdown test would help too.
Many people with average mechanical skills have been successful, however the few that run in to issues need to be open minded about the many possible mistakes that can happen by either human error or bad parts in order to solve the problems. We are always here to helpMan a cam change sounds pretty difficult after reading all this. I was pondering if I could swap my heads and maybe do a cam swap but thinking this might be above me.