k3500 silverado vortec 454 possible fuel pressure regulator?

[justasquid]

I have a 97 silverado 3500 with the vortec 454 in it. It has 200k on it, and has a horrible low throttle input miss and a high idle at times. It is also way down on power and stumbles until you really give it some gas, but even then, you can tell its low on power. Unfortunately, this is how I aquired the vehicle with this condition. I changed the plugs, wires, fuel filter, and even the distributor for the common worn out gear, and man was it worn. Everything I changed was extremely worn out and each time, I though for sure I found the issue. but the issue is still there. In fact, it seems to hesitate even worse now. I do now have a p1345 code (crankshaft/camshaft correlation) since I changed the distributor, but have read that it can only be adjusted with scan tool. I do wonder though if the distributor was the issue and I have it one tooth off. I made sure to mark everything and put it all back. But I don't know 100 percent sure it was correct to start with.

My main question now is: what is the fuel pressure suppose to be? With the fuel pump on, it registers around 50 psi. As soon as the fuel pump shuts off, it drops to 20 psi. But will stay there for hours. I have read that it should not drop at all and if it does, the FPR or injector could be the issue. I have read these engines need to run at least 60psi, but have also read lower psi.

I guess I need to buy a service manual. But if anyone has had any experience with these engines and can point me in the right direction, I would greatly appreciate it.