96 Tahoe stalling running rough not starting

My 96 Tahoe has been having problems for a couple months now and it's getting worse. It started out just an occasional miss then hard to start (especially when warm). Now there is no power when I punch it and it will stall out when I shift it into gear from park. Sometimes I can't get it started at all. I started out replacing the fuel pressure regulator (@50psi running). The psi is now @59. I also just replaced O2 sensors, plugs, wires, cap, rotor, coil, and the control module that is mounted on the same bracket as the coil. At this point I gave up and took it to my local mechanic and he replaced the fuel filter (was replaced 6 months ago) and said it was fixed. I drove off and still have the same problem maybe a little better. Any suggestions? I'm thinking maybe the fuel pump (replaced about 4 years ago by GM).:banghead:

Look at the post from MT-2500 in this thread http://www.automotiveforums.com/vbulletin/showthread.php?t=504349

and post back the pressures.

//2000CAYukon

I am getting 59psi when running and no fast leak down when turned off. I haven't checked the pressure when driving, cold start, or with the return line pinched. How do you pinch off the return line? It is a metal tube. I will have to post the other pressures later (truck is in the shop). Also now I am getting 2 new codes P0171 and P0174 (fuel trim system lean bank 1 and 2). Another thing to add when I replaced the fuel pressure regulator I removed the 2 yellow o-rings that are down inside where the 2 fuel lines go in. I thought these were the 2 fuel line o-rings that come in the Felpro gasket kit I bought but come to find out these are the wrong ones. I got the correct o-rings from GM but can't get them down in where they were before. Now they are sitting up on the first ledge which makes the fuel lines sit a little higher up. I asked my mechanic about this and he doesn't think that should be a problem as long as I'm not leaking fuel, which I'm not but I wasn't having the stalling problems before.