DJtheKID

Hello I'm new to this sight and I really need help. I have an 09 Silverado with the 5.3l. It's currently throwing codes p0300 and p0135. I took it to a shop yesterday it was only throwing p0300 and is was in ol fault. I paid for a diagnostic and when I got it back it was only throwing a p0135 and the o2 sensors was in hooked but it was now running fine. I bought a new o2 sensor and replaced the old and that still didn't fix it. I unhooked the o2 sensor again and now it's also throwing the p0300 code so I can't even go to the store. I'm not sure what the mechanic did yesterday to get it to run. I checked the voltage to the wiring harness and it's getting 12 volts also Checked the ground and it's was also 12v. the resistance was showing around 80 on the multimeter. around a week ago it started missing horribly and I pulled off the road my cat was red hot so I had to replace it because it was destroyed. at the time I had a p0300 code and a p1682 code. I'm completely lost I've changed the plugs swapped coils and wires new manifold intake gasket and cleaned it out since it was full of oil. I've tested the map and maf sensor. but all of the misfires are coming from bank one. at idle it misfires on 7 but when u give it has it spreads out to the other three and stops misfiring on 7. is it possible that it's in the ignition or the pcm? I'm totally lost and basically out of money at this point. Any help would be extremely appreciated.