2003 mercruiser 5.0 efi wont go over 1800 rpm.

I own a 2003 rinker with a 5.0 efi bravo 3 outdrive. My problem is when I put it in the water you full throttle runs good for about 10 seconds then boggs down and pops through the throttle body, so u have to let off on the throttle and nurse it running. I had a similar problem last year and had only 18 psi at the fuel rail so I replaced the fuel pump assy with the updated kit. It ran fine for about 2 months with the new pump i had 38-40 psi at idle. i have since replaced the cap rotor and have had the boat computer tested no codes. I currently have 38 psi running. Is this enough pressure ? If you turn the key on and off and cycle the pump for a few times it will runn fine for about 10 seconds. I am thinking pump again but am trying to figure out y it is going bad again. I have also replaced the lower water pump before the pump went bad. Help i need my boat.