Well I am having a problem with my fuel pressure when I leave for work in the morning it is cool out the fuel pressure stays fine. When I come home from work and it is hot out my fuel pressure goes down a lot lower when I really get into the throttle and loses power why is this. When it is cool out it runs like 40psi and at wot throttle it might go down to 30psi. When hot drops from 40psi to like 20psi when wot.

 

When you installed the '99 engine did you change the fuel system to the '99+ returnless type, or retain the stock return type system.

If you kept the return type I would first suspect that the fuel pressure regulator is defective; if you changed over to the returnless system then my first target would be the fuel rail pressure sensor...

 

I took all the fuel stuff from my 97 engine and put it on the '99 engine.

 

Then I would suspect that the fuel pressure regulator is bad.

With the engine running and at one of those times when it is hot as you describe, what happens to the fuel pressure when you remove the vacuum line from the FPR (plug the line)? The fuel pressure should rise quite a bit.