Please help! I have a 2019 xlt 5.0 that is throwing P0420 and P0430 codes. I have replaced the down tube system with new cats and have replaced all 4 oxygen sensors. I have cleared the codes after replacing the parts and they keep coming back. Any idea of what would cause this?

 

A poor air/fuel mixture can cause this and fuel mixture is affected by lots of things. Do you have any other codes?
Is your engine coolant temperature (ECT) indicator reading correctly? Should read approximately mid-scale.

 

no other codes. If i clear the coded it'll run good for maybe 20 miles and then throw the codes and start bogging down when accelerating. Coolant is good and maintains mid range temp.

 

Did you use OEM or aftermarket cats? Did you replace them for this issue or for some other reason?

 

Clean the MAF with cleaner, don't touch the filament. Report back.

 

I'll bet money the OP has aftermarket cats, and he'll find they're 'EPA legal' and 'will meet FEDERAL standards' but are only '46 state legal'.

 

I’ve had similar issues with my 2019 2.7L. Drove me nuts for the past several years. What I have learned through trial and error is that topping off the gas tank can contaminate the cats. No idea why but when I stopped topping off the tank my check engine light stayed off. After several months I mistakenly topped off the tank and the code came back.
This might not be your issue but it’s simple to check.
Good luck.