I just put headers on my 94 camaro z28 lt1 and now I am having a lack of power and a pretty good bit of missing I also deleted the cat and smog pump could deleting these cause missing? Or is it more likely spark plugs and wires not on right

Did you buy "non-emissions" headers? Was EGR deleted also? New plugs/wires or did you keep the old ones? Long tubes? If so, how did you extend the O2 sensor harnesses?

Pacesetter Mid length o2 was long enough I plugged the air holes but used the egr I did use old plugs and wires but they were put on 3 months ago and we're iridiums it ran perfect before header install now it's got a loss of power and a bit of missing

At this point, just a lot of suggestions on things to check:

-Are the AIR connections sealed air-tight?

-Did you check header flange surface for flatness?

-Are you sure there are no exhaust leaks at the header flange?

-Did you reuse old O2 sensors? If so, did you spray them with rust penetrant to break them loose? Did you possibly contaminate them with an excess of anti-seize? You mention "o2".... I'll assume you mean "O2 s" (plural)

-Is it possible you knocked a spark plug boot loose?

-Is it possible you hit a spark plug and cracked the porcelain?

-Is there a plug wire or O2 sensor wire against the headers? They will burn quickly.

-Did you keep the metal plug boot shields?

-Stock plug wire routing, or OTVC?

-Is it possible you switched two plug wires?

-Did you remove the air intake ducting to remove/access the AIR tubers, possibly forgetting to reconnect the MAF or knock the wire off the coolant temp sensor?

-Is it possible you knocked the harness wire off the knock sensor?

-Is the SES light on?

I have done most of those checks I had forgotten to region the maf sensor and it at least turned off the check engine light I reused one o2 sensor and replaceed on with the denso version wondering if that crappy o2 sensor could be causing my problems