Greeting all! Long time lurking, first time poster.
Here's the specifics first: 2004 S type, 3.0 Base sedan.
Work done over the last year: Replaced Cat Convertors, replaced O2 sensors, replaced Fuel Ratio Sensors, replaced plugs and ignition coils, replaced fuel pump with a reclaimed one from a 2003 Jag S type.

The issue I am having now is that while the engine is cool, it runs fine. Once it warms up, at 3000-3500 RPM, it bogs down and wants to die on me. The fuel pressure at the rail averages 53psi. It will occasionally drop to 40 when hitting the gas hard. (this happens when cool however.)
This is driving me nuts, to the poorhouse, and may drive me to divorce court! (My wife loves the car as much as I do!) And while the Government claims the economy is wonderful, unless you know the secret millionaires handshake, it sucks here in Florida.
So any advice? And no, I am not a mechanic, so please keep the answers as..... well, simple as possible. I have the workshop manual, it's written in Klingon, but if told "replace a, b, c," I can do it. Generally, kinda, somewhat....
Thanks for the help all!

 

oh, and since I forgot, I do not get any codes.

 

Isn't fuel pressure supposed to increase at full throttle, the opposite of what you're seeing? That could explain a lot.

If so, the trick would be to determine if the pump is weak, or it's getting an inaccurate command such as from a bad fuel pressure regulator. IIRC, the regulator looks at intake manifold pressure, so maybe the fault is as simple as a vacuum leak. These are all just thoughts off the top of my head, so wait for the experts to chime in.

 

You could look at fuel trims. If there's a fuel (or air) problem it will show in those in under a second.

 

Change the fuel filters?

 

Yes I did, I should have said that in the beginning, but alas, there's no edit function for me.