stated out a lifter rattle sound and or piston slap common on gm motors found that is was coming from drive side cat rattle got worse and not loss of power under hard acceleration with flashing cel and only a p0300 misfire code the cel goes off and after a few minutes still driving untill accelerating again it wont go over 4000 rpm having the pedal to the floor thinking it might be cat on drive side could it be anything else?????? also got a mass air flow code has the 5.3 2 wheel drive

thanks for your in put and help

 

clogged cat I'm assumin. Take it off and replace it if need be.