Oil pumps breaking

2000 silverado 6.0 liter I cant keep
a oil pump in my truck. It keeps
breaking oil pumps. I mean
actually the pump breaks in
pieces  I have to put my 4th pump.
Why ? I've pulled the oil pan each
time cleaning debris from pan.
Inspected pick up tube and screen  
put correct oil ring on tube to
pump  primed pump  it last for
about 4 to 6 months. I've checked
thrust bearing to ensure crank
shaft is not moving back and
forth.  Why or any ideas why this
is happening o yes I also flushed
engine each time and  hacked
bearings. Other than the pump
problem the truck runs great
I've always had  noise in the valve
tran until it warms up oil the oil
flows. Oil seams to drain  back in
pan and pump has to pull oil in
engine to quite it down. To .much
drain back.
G M will not acknowledge that
these engine oil pump problems
and valve train noise. All have this
problems  if they acknowledge
theirs a problem they would have
to recall and fix it. They wont do
that  they also say that the 6.0 liter
is a  non interference engine that's
a lie and  I can prove this  anyway
any answers would be great  I love
this truck