99 gmc 5.7 vortec hard to start when it is warm doesnt do it always run for awile the shut down 15-30 min try to start backfires hard to turn over misses when it does start it runs ruff till you take it out on hiway it will do this if you start it and let it idle a long time once in a while it wont start untill you let it cool down a long time new fuel pump cataletic converters 02 sensor no codes runs good starts good cold