Ways for checking fuel pressure loss are on my website. You should always start with diagnostics and not just guess by replacing parts.

 

It could be a leaking injector. Gasoline is a non-compressible fluid. It only takes a few drops of fuel escaping from the tip of the injector to cause the fuel pressure in a static sytem to drop. This small drips may not be large enough to affect the running of the engine to a point where you would notice it... and not enough to cause a misfire code.

And a small amount of excess fuel from one or two injectors can simply cause the PCM to make minor corrections to the long term fuel corrections. Again, not enough to set a code for excessive long term fuel corrections.

The only injector code is based on the voltage at the injectors, and requires an order-of-magnitude problem like a shorted injector or an open circuit to set a code.

 

Yea I know I had an old regulator off an engine that I knew worked so that's why I swapped it out.
I would never just replace parts.
I pulled the fuel presser rail off to see if the injectors were leaking and just my luck not one drop came out of any of them.
There is no gas leaking from any of the lines either.
So now I guess I have to pull the tank down and replace the pump again.
I guess I got the one pump in god knows how many that's got an internal failure in it.
Then Pump has warranty on it so threes is no problem there.
Is there a Co. that makes a gas tank where the neck unbolts off?
Because that's the only problem I have with taking the tank down I always have a big problem getting the neck back in.
Lent me know.
Thanks,

 

Read the last paragraph of post #15.

 

So I got the tank down and the fuel pump out and you would never guess what the problem was.
On the quick disconnect for the supply line in the tank from the pump to the metal line I was missing an O ring!
I had replaced the sender with a Delphi one a while back and it had 2 O rings on the supply line the OE one only had 1 O ring.
I guess when I replaced the pump the last time I must have dropped the other O ring.
So I replace both O rings and it's fine.
Lesson learned.

 

And there ya have it. Congrats.

PS - why didn't you elect to cut an access panel as mentioned? Would have saved you a ton of work.

 

Ive pulled the gas tank down so many times between my 97 and my third Gen that it only took me an hour and a half to get it down.
I just don't like putting big holes in the car and if you don't run the tank low your not going to be replacing the pump often.
I learned that lesson.
But it the gas tank neck beat the crap out of me trying to get it in.
When I get some money together I'm either going to find a way to make the neck bolt on or I'm going to buy one of these and kill 3 birds with one stone.
LT1 F-Body Sumped Race Tank - Nasty Performance Parts For Cars, Trucks
One the neck will bolt on and off.
Two the fuel pump will be outside of the tank.
And three the fuel gauge will read right and not go up and down when you hit the brakes and take off.
But that's not going to be for a while because my 71 Camaro is getting it's body and paint done and that's where every penny is going right now.