i have a 2002 ss that under full power fall flat on it face between 5500-5800 rpm in the lower gear . Do not have a clue , why?

You’ll prolly need to data log to see what’s going on.

I do not have the ability to do that
and to the question what it like after 5800 rpm the power come back like gang busters all the way to rev limiter over 6000

It is fuel injected total stock 2002 SS

There is only 12000 miles on it, there is no poping noise it is all quiet when this happens . I have complained to GM in the past about it.

Thanks I will check on the vavle springs .

Id find a tuner that can do this for you. Your just guessing and throwing parts at it until then.

That is my plan . Could you hear ignition knock at 5500-5800? I will get it tuned but I wonder if the knock sensor is picking up ignition knock and pulling timing back

Depends on exhaust and other factors. I’ve seen improperly setup valvetrain cause the knock sensors to pull timing.
I’d be more interested in the tuner logging everything to find the issues, than actually looking for more power, but why not kill two birds with one stone. Keep us posted.

Will keep informed
it totally stock ( black wing air intake and filter and daul daul exhaust and 3inch exhaust pipe. Slp called it the ( 345 hp kit )

Filter been changed
got spark plugs to change
does anybody know if the rev limiter work on 3/4 throttle or just full throttle?