I just got all these same symptoms on my 2011 Tahoe 5.3 was about to get on the forum and ask the exact same questions. Recently had the exhaust manifolds redone and I was going to start by checking the bolts. At cold start it sounds like an exhaust leak, warms up and then doesn't sound like exhaust leak, then ticking for a bit then that goes away. My neighbor ex-mechanic thinks its a lifter and recommending pulling the oil filter and checking for shavings. Suggested cutting the filter in half but I'm thinking this would cause shavings to appear. I was traveling yesterday at 73 mph and my oil pressure was at about 28 psi. If I recall correctly, seems like I've always had a steady 40psi.