Lost and need help.1993 ZR1

[Route 66]

I have a problem with my 93 ZR1. I have not been able to get the 405 HP for some time. I haven't had the time to work on it again tell now. I started trying to find why I don't have the 405 about 6 to 8 years ago. Thought then it was because of vacuum leaks under the plenum. Pulled plenum and repaired all the leaks. Checked actuators they seamed to work like they should. Installed new vacuum solenoid. I put it back together it did not solve the problem. So I left it tell about a week ago and started once more to find the problem. Checked fuel pressure will not go higher than about 43lbs psi at 3000 RPM. After shutting the engine off the pressure will drop to about 15 psi in about 1 hour. Replaced fuel filter. Also while I had the fuel lines open I thought I would check the Y hose connection in the tank. Pulled the Fuel pump. I had put a new GM ZR1 fuel pump assembly in when I worked on it the last time.[6 to 8 years ago] It still looked as new as when I put it in the tank. I don't think it would be leaking pressure there. All hoses and fittings looked good
One more thing I am not getting any Check Engine trouble codes. I get the 12 code. I was getting a service LTPWS. I solved that problem. Plus I don't think there is a connection between the 2. Now no Codes and no 405 HP.
Your help would would be most appreciated Thanks Ellis

Took this picture today of the pump I installed back then. I am not sure but I do not think this is my problem.