Here's my experiences:
I've had a 2002 gmc yukon with 5.3L, made lifter noises when first starting, especially when cold outside, since i got it with 90,000 miles. Oil pressure is over 40 psi at idle, mobil 1 oil changes. Engine runs great.
The 2007 suburban with 5.3L with cylinder deactivation ate 3 qts between oil changes, got an oil warning light, oil was low so topped it off. OIl light still on. Checked oil pressure with mechanical guage, its a pain the first time since at the back of the intake near firewall and is done by feel, pressure was fine, replaced oil pressure sending unit with AC delco and screen below it (use a bent pic to remove, they are cheap so buy two just in case you lose it)...fixed problem...probably got clogged when i ran it low on oil.