I have an 06 Silverado 5.3. The o-ring on the oil pickup tube has been going bad . I've been driving it with some ticking from the lifters which goes away after warmed up and pressure comes up. Until now I'm on a trip with 9 hours to go and pressure started to drop more than usual . My question is can I overfill the oil to submerge the o-ring and be able to get where I'm headed safely?
First, I doubt your o-ring is bad. It doesn't work that way on these engines.
Second, the o-ring is located just below the centerline of the crankshaft. To get the oil above the o-ring, you'd have to fill up the engine with enough oil the crankshaft would be hitting the oil, which would damage the engine.
These earlier LS engines are fairly notorious for having lifter noises when the mileage gets high. It usually stems from the pressure relief spring in the oil pump getting weak. When it does, it allows the oil to bypass more than it should. This shows as a drop in oil pressure as well as you may start hearing a little bit of noise out of the lifters. The only cure for this is to replace the pump (even an OEM pump works just fine). When the engine and oil get hot from long driving, the noise may be a little bit louder and the pressure may be a little bit lower than normal.
Depending on what you're seeing your oil pressure reading, there's probably no "big" issue here. Yes, it is a little disconcerting, but unless you're towing something (which would cause a larger burden on the engine), you shouldn't be in any danger. The engine can function just fine. Depending on what your oil pressure is reading, 15 lbs is more than enough to service the engine.