Power loss at half to full throttle?

[TinysTurboPerf]

Car was getting harder to start and longer cranking, so normally
it would be the fuel pump. Also, when driving, the car would run ok and boost seemed ok, until past half throttle or full throttle. Then the car would seem to miss and lose power. Well I just installed a Muscle Pump that I bought a few years ago from Modern that I had never used. Well the car holds fuel pressure now and starts easily, but it still seems to have a problem with losing power and seems to be missing out at higher rpm's.

Any suggestions would be greatfully appreciated.

TINY

 

[MeanBuicks]

Do you have a scan tool?

It would help to know that the MAF, TPS, O2, etc. are reading correctly. You could also monitor KR.

Also, are your valve springs original?