It's possible the cam was installed just by simply lining up the dots. Very often that could mean the cam is installed/timed retarded. Specially if the timing gear isn't ground/marked right.
A 'late' cam will shift the engine's powerband to a higher rpm, which could explain your findings.
Degreeing the cam will tell the true story here.
I had 383 once in which I purposely installed a retarded timed cam as a test. The engine couldn't spin a tire on wet pavement from a stop, but once rolling and the engine got above around 2000rpm it would break the tires loose.