Hey everybody, I have a 2000 Silverado 5.3 with the codes P0171, P0174, P0420. I am completely stumped right now. My mechanic replaced the intake manifold gasket, which was blown, as well as the MAF. I know P0420 is catalytic converter but here's the thing. The truck, after having all that replaced still wants to stall in the garage and whenever I try to take it over 2000rpm is acts likes its dying. I also ended up replacing my EGR valve and cleaning the IAC and nope, still runs like crap. But the real kicker to me is that the stalling and everything is intermittent. I also believe it does it more when the tank is less than half. It the original fuel pump with 193,000 mi on it. So I'm not sure. I read that the catalytic converter could cause it to stall, but would that be intermittent? Someone help! I'm not sure where to go now. I don't have a tool to test the fuel pressure and I'm not sure that I want to take it back to the mechanic since he didn't fix it the first time. My next question is what is the average reading from a MAF? I bought a scan tool with live data and it generally pulls 3.6-7.8gr/s. I also changed the PCV and inspected all hoses. Thanks!