First a question.
Did the motor misfire above 5000 before this cam change?
If it DID the problem is not in the cam change or springs pressure etc more than likely something else I.E. electrical bug somewhere in ignition.
If it did NOT misfire before then its definetly pointing to something in the cam change.
I. E. incorrect cam to crank alignment or inadequet spring pressure, improper valve installed height etc.
Sounds like not enough spring pressure for the cam to me, and just because the springs are new as you say in the motor doesn't mean they have the right spring pressure required for the cam you installed.
Its always a good idea to install new springs ANYTIME you install a new cam, saves headaches and give peace of mind when you do run into roadblocks such as this by simply eliminating major things like springs right off the bat.
However it could be something as simple as a cam being out of degree, I'd double check that then springs next.
Goodluck, Charles