I finally got my LS1 Darton motor back together and it ran great!! I broke it in gently over 3-4 months of cool weather, like in October, November, December, & March. No problems-it ran great, and now has about 600 miles on it since rebuild.. On March 6, wife and I drove it about 15-20 miles to a bank branch in the country, to get a few more miles on it. After finishing up at the bank, we got in, fired it up, and drove about another mile when all of a sudden, with no prior warning, the oil pressure took a nosedive!! The motor never knocked or had any valvetrain clicking, but I still reached for the key and shut the motor down immediately after the preesure started dropping. Towed it home and checked with a mechanical gauge to ensure that the cars electronics were NOT giving a false readout. Before this problem, the motor had 60-70lbs. pressure when cold, and 40-50lbs. pressure when hot, as measured at idle speed. The mechanical gauge showed about 20 lbs at idle now when cold, and at 2,000-2,500 RPM it hits about 40lbs. pressure. The motor only ran for about 10-20 seconds total. I shut the motor down and re-started it about 1 minute later, Obviously, the motor was still cold at that point. This time, I got 0-maybe 5lbs. pressure at idle, and when I revved it to 2 grand, it went up to only 20lbs. pressure. I shut it down after maybe 5 more seconds of run time and have not fired it since, as I don't want to ruin it. I am running the Melling higher volume/pressure oil pump, and this same pump was in it for 30,000 miles with no previous issues. And it DID RUN good this time for better than 600 miles. Since the motor is NOT knocking and is just starting to have a slight increase in valvetrain "clicking", I believe that this is some sort of oil pump issue, as opposed to an internal engine issue, especially since I covered over 600 miles without any problems.. I was thinking that the O-ring may be bad, but the more I think about it, I am leaning in the direction of the relief valve being stuck. What do you guys think? Any help would be greatly appreciated. This motor is in a C5 and I am trying to think of a way to do this without dropping the whole front cradle out of the car. I have a 2 piece timing cover, and I wonder if that would allow access to the relief valve without dropping the cradle. Any help would be greatly appreciated! Please advise.