I just put my stroked 4.6 back in my ride and I have a 2.6L KB with 9 PSI and the thing dynoed at 350 RWHP NOT GOOD!!!!! Installed a 12 PSI pulley and it lost 10 HP. Dyno shows correct A/F and all peramiters are in line. It is producing the correct boost for each pulley. I ran this S/C on the stock 4.6 and it seemed to have a lot more power than the 5.0 thats in it now. Only changes I made besides the larger cubic inches were the Comp Cams VSR got rid of the Boost a Pump and went to the GT500 Fuel pumps and tuned for 92 octane. KB says look for restrictions in the intake....I did all that and found it to be free flowing. PLEASE HELP!!!

 

It seems like when there is an issue like this the usual suspect is the fuel system. Thnigs that can go wrong with the fuel system.

Bad pump
Wiring
lines fall off or break
a fuse blows

These are just guesses.

I would data log a run on the dyno and have someone who knows what they are doing look at everything to see what the parameters are.