Aight, thats just me being frustrated that I can't help you fix it so far
Ok, so even if its a new regulator, we've thrown out all the easy stuff, time to start looking at the less-likely problems. I'd see if you can trade the reg in as defective, just to try a new one to look for improvement.
Might be worth it to doublechekc the fuel pump wiring and make sure it didn't ground out or come loose or something like that....my brain hurts on this damn thread...I need your truck running.