Damn man. So fixing the return line brought down the fuel pressure......
I noticed everything you have changed and I am at a loss....
Have you taken the negative off the battery since the drop in fuel pressure.....
What codes are you still getting......What are your O2's and are you getting any knock...
Everything I can think of you have already changed...
Just for the hell of it, pull the MAF and take a look at it and clean it with some intake cleaner.....