2001 454 MPI Hesitates on Take Off
 

I just replaced a head on my friends boat due to overheating. Everything is good, idles great, good compression. Revs good with no load. When I take off I have to use the Tabs to get the bow down and then it shoots off like a rocket and runs perfect. It hesitates something awful on take off. I checked the fuel pressure and at idle its 40PSI. During take off trying to plane, it jumps erratically from 40 to 28PSI and the needle is moving very quick. Once on plane, cruising or WOT, its a constant 40PSI and doesnt change until I try and take off again. Does this sound like the fuel pressure regulator? I checked vacuum at the port where the regulator line is and vacuum is good also according to Merc manual 23.