99 Suburban Misfire
 

I have a 99 Suburban with 5.7L V8. Bought it last year with 155k on it and ran great for almost a year. Started misfiring bad and discovered cat on passenger side blown out. Replaced it along with fuel filter, plugs, wires, cap, rotor and still having misfire. Have an OTC computer to scan codes and engine diagnostics. Current codes are P0300B, P0155, and P0101. While watching engine test with it running, always misfires on Cyl 4 and 6. Mass Air Flow is at 9 g/s at idle. Misfire is noticeable at all times, but smooths out some at highway speeds. Gas mileage is terrible and gas smell is very strong at idle in the driveway. Can test almost anything with the computer I have, but have nothing to tell me what is acceptable numbers. Any help I can get is greatly appreciated as this is my wife's daily driver!!