GMC Repair: ramdon miss firing, ramdon, rough run

Question
i have a 2001 sierra 5.3 v-8.
it started lossing power and miss firing i had them run a dinostic check on it. al it read was ramdon miss firing cyclinders 1-3-5-7. mechanic thought the fuel rail might be clog up i took them of and there clean. fuel pump is putting out 50# i know it should be 55-62 any ideas. i did put new plug air filter-gas filter and had the injector system cleaned

Answer
HI,Walter
 50 psi is ok,but a bit low,is this pressure when the truck is running?also usually with missfires in cyl 1357 which is one bank /left bank,i think you have a plugged catalytic converter on the left side,if the cat conv is plugged it will cause a rough run,missfire and lack of power,i would back pressure check at least the left bank and see if its excessive,i would bet it is and you have a failed catalytic converter that is causing your complaint.if you need more help contact me.Thanks

ED