ok just rebuilt the motor 2000 miles ago .put every thing new in sensors in it
car ran rough scaned car got these codes
p420
p430
p300
p400
i replace the egr valve with ac delco. but do the codes for the cats mean they need to be replaced ? or does it mean the o2s are going bad . i have bosh
o2s .or is the miss fire causing the cat codes.opt is new plugs are new wires are also new summit wires. any help would be great

 

I have yet to find a GM vehicle that can use Bosch O2's. Mine included. The way it was explained to me is some companies don't actually make the O2s but specify O2's that operate in wider range than some vehicles can tolerate. This way they can purchase fewer part numbers from the actual manufacturer and save money. This however, causes fits with some vehicles like my Z71.

Your egr system may be the source of the entire problem. If it's feeding exhaust gas when it should not be, it could cause the CAT efficiency problem and the misfires.

Try disconnecting the EGR valve and reset the codes to see if the 300 and the 420, 430 does not return.