99 5.3l Misfire

[stvdalton]

OKay guys, I have a 99 Chevy 5.3L z-71. I like the truck, but having a/c problems also, but that was on another post I had. Ha! But for the main problem, having a mis when mainly at idle, intermitent though, after a minute or so I can smell rich fuel/exhaust and it is misfiring bad. Like I said, sometimes it won't though. then sometimes when at highway speeds and then I give it a little gas, it will kinda shutter a little, then be fine. Well, I didn't think my service engine light was on, but it is actually burned out autozone said. The codes were these:

P0300 RANDOM MISFIRE ON ALL CYLINDERS

P0420 CATALYST EFFICIENCY LOW-BANK 1

P0430 CATALYST EFFICIENCY LOW-BANK 2

P0440 EVAPORATIVE EMISSION SYSTEM

 

Autozone guy says, something with fuel system, anything from fuel psi bad, fuel filter, possibly 02 sensors but proably not since both banks, vacuum leak, catlytic bad,fuel psi regulator, injector problems, intake manifold leak, okay I think that was about it.

Said he really didn't think it was plugs/wires problems, for one they were changed 30k ago.

But the fuel pump was changed 8k miles ago and fuel filter same time. Should I still get fuel psi checked first? Where do I start, I also have the truck for sale, I'm telling people that look at it that it does have an intermitent mis also. Maybe someone else will buy this thing, but I'm being honest with them about me having no idea what the mis is. Help. Thanks!

[Lifted 2000 Silverado]

My 2000 would do that it was the plugs but I dont recall if any codes came up, I dont think they did.