03 Silverado 5.3 motor knock/oil issue? Need help

When I crank my 03 Silverado 5.3 up,
especially a cold start, the motor knocks and
it slowly goes away until the motor is warmed
up some, sometimes it will only knock for
about 1-3 seconds after starting up, which
I’ve heard from others in some cases can be
normal with these, however this is not the
issue here. Once the truck is warmed up and
on the road the motor sounds perfect, no
ticking or knocking whatsoever. If I come to a
complete stop for more than about 2-3
minutes the knock slowly comes back and
gets louder as time passes, so I’ve came into
the habit of just turning it off if I make any
quick stops, and if I drive down the road it will
slowly go away. Sometimes I can sit idle and it
won’t do it at all and it runs perfect. I’m
worried this is going to end up causing some
serious damage to the motor and I can’t trace
the cause of it and I’ve taken it to a couple
mechanics that scratched their heads, now
this truck does have 267,000 miles, which is
pretty up there, but besides when it acts up
the truck runs fine with no issues, sometimes
the truck will go into the “Reduced Engine
Power” mode and I have to cut the engine for
about 60 seconds for it to go away. I have a
check engine light on for the knock sensor 2,
which I wouldn’t assume that would be the
cause of this. But my oil pressure gauge
jumps from either all the way down at 0, or all
the way up to 80, but normally stays down at
0, and jumps back and forth periodically, l I’d
assume that’s my oil pressure sensor that’s
gone bad but it doesn’t throw a code for it.
Could the faulty sensor cause issues with my
oil pump? Or does that sensor/gauge have no
effect on the oil pump? Could this mean my
oil pump is going bad? I’m confused at the
entire situation, if anyone has any experience
or any suggestions please let me know! One
guy said it could be the oil pump inlet o ring,
but I just replaced the oil pan gasket and
replaced that while I was down there, so that’s
not the issue. I’ve been chasing this problem
for awhile and it seems to be getting worse,
and I don’t want to cause any harm to the
motor. Thanks!