What is the fuel pump pressure for 3800 Series 1 engine?

I believe I have low fuel pressure on the vehicle listed above with a 3800 engine. With key on my new gauge reads 32 lbs and when I start the car it drops down to 26 lbs. After shutting the engine off, the pressure will rise to 32 lbs. Pressure will fall only to 30 psi and stay there for about four hours before slowing bleeding off. I have replaced the fuel pump and both filters (in tank and outside tank) with original OE parts, and also have replaced the fuel pressure regulator but still seems to have low pressure. So what is the key on pressure and engine running pressure for this series l 3800 engine?

My original problem with this very low mileage car is it would not stay running and I foolishly replaced the pump and filters which did nothing to help me. Then I replaced the pressure regulator (which was the problem) and now it will no longer stall and runs decent however, I am concerned I may be running a bit lean still. I have an Oldsmobile service manual; however, I find that in one section it states the pressure should be 24-36 psi but then in another section in the book for the 3.8 engine it says key on 37-43 psi and at engine idle 5-9 PSI less. The engine doesn't idle as smoothly as some other 3800's I have owned in the past and I am concerned it may be a fuel pressure problem. Any help would be greatly appreciated.