I think your best bet is to pull them and get new hoses put on your lines--that's what I've done with similar lines. The quality of replacement parts these days is hit or miss.
Sounds like it could be a weak fuel pump. My factory service manual says my 97 vortec 5.7 needs over 60 PSI while running (if I remember correctly).
It could also be a bad fuel pressure regulator. You can clamp off the rubber return line slowly and see if pressure builds. If it does, that...
I got fans and shroud from a LT1 F body (93-97) for two of these trucks (including my current one) and they fit great. I made some simple brackets for the top and the bottom fit into the shroud like it was made for it. I used a flexalite control kit for this setup, but the last one I just ran...
If you are not getting any knock counts, I would check and see what your MAP and TPS sensors are doing at the time of the change in timing. A drop in MAP gets you pretty close to timing levels you are seeing.