Engine power

[Big hammer]

I just installed a rebuilt engine, doesn't have the power I think it should have.
Thinking out loud, is this a case if it isn't broke mess with it until it is?
Sometimes fresh engines don't seam to preform like we think they should !
Iam for drive it, get some miles on it before we condemn it. Just maybe when things become happy in their new home, it will be better! Optimistic Big Hammer :-)