My 96 Chevy Silverado K1500 5.7L v8 slow on acceleration

I have a 96 chevy Silverado K1500 5.7L v8 at
approximately 250,000miles. A few weeks ago I let
my truck sit for like two days without
driving/starting it so when I did go to start it, it
wouldn't start so I changed the starter and it
worked again.  After changing the starter a few
days later the truck started acting like it didn't want
to accelerate after pressing on the gas. It would
accelerate but after jumping real hard and taking a
minute to reach speed. Then the check engine light
came on so I had auto zone check the light.  They
said the code came back as the o2 sensor,  so I
changed the o2 sensor. Still the same problem,
there was no difference.  So they had me put a fuel
cleaner in the truck (seafoam) still no change.  I
have changed the PCV value, mass air flow sensor,
the fuel filter, starter, plugs and wires. After
changing all of that it is still no difference in the
truck. Also now the code for the engine light is
saying a lean head. I don't know what that means.
Does anyone have any suggestions?