2004 Silverado 1500 4.3L misfire issue

I have a manual 2004 Silverado 1500 and I seem
to be having a reoccurring misfire issue. The truck
occasionally (not everytime) will struggle to make it
up hills when I’m accelerating. It appears to lose
power and the stick shift starts violently shaking.
Occasionally it will cause the check engine light to
start flashing for a few minutes as well but not
every time. The issue seems to come and go.

I recently took it to a mechanic and they put all
new plugs, wires, and replaced the distributor cap
and that didn’t solve the issue and I took it back
and they installed one new o2 sensor for me. The
truck ran fairly well and the o2 sensor seemed to
have solved the problem for a few months
however now it’s starting todo the same thing
again.  

I’m not sure what to look into fixing next. Any
information would be greatly appreciated!

Thanks