Next step advice

History:
Suspected a head gasket leak for some time.
Have changed all coils and spark plugs in recent years but have not tried replacing them all again. I DO need to pull some plugs and inspect.
Began getting a "shuddering" at speed and low idle at stops. Ran some fuel system cleaner through just before this began.
Got a misfire on Cyl 3, tested coil, replaced, code hasn't come back
Cleaned MAF, tested MAF by unplugging while running engine- result, engine shut off.
Threw some codes pertaining to both O2 banks Cant remember but i believe they were P0171 and p0172, and Cat running below efficiency levels, P0420, P0430, All this came at once.
Checked for vacuum leaks and have not been able to find any.
Replaced all injectors. seemed to make things run smoother but am still getting the shuddering while in closed loop condition.
Latest codes are P0420 bank 1 and P0300 with a pending P0430 on bank 2
Should, I go ahead and changeO2 sensors or A/F, rather?

** just went out with engine warm and got a misfire on cyl 2 at ldle. This one has a new coil in it. Im guessing its likely just a horribly bad head gasket leak that the Bar's Sealer didn't help with. Sigh.

 

If you think you have a head gasket leak, have you done a compression check? Have you read the plugs for signs of coolant contamination?
Don't use stuff like Barr's, it will just make a mess of the cooling system and futz-up your water pump and thermostat. Start with the basics; plug color and condition, compression check, and vacuum readings and consistency. So it has vacuum, does the signal flutter at idle or steady RPM? That can indicate a burnt valve. Have you tried looking into the cylinders with a diagnostic camera? Have you lost coolant or oil? Have you looked at the valvetrain to see if you have any rocker, pushrod, or spring issues? How are you checking for vacuum leaks? Those can be a pain to track down.