I have a 1999 Suburban 5.7 L V8 which has been very reliable. It has been running for a while with a soft check engine code P0430. I have changed the oxygen sensors and nothing has changed. Lately it has developed a violent miss/backfire only after warming up and being driven a distance. Battery, alternator, thermostat, distributor cap and crank position sensor have been replaced. What is the next step to figuring this out? Thanks.

 

Could be the fuel pressure regulator going bad. It is located under the upper intake attached to the spider fuel housing where the plug attaches. If you have a scope camera use that to look to the back of the intake signs of leaking.