Misfiring codes creating a CEL
 

Hi All. I just recently had my 2000 A6 4.2 Tip transmission rebuilt because I lost reverse. Since I got the car back, I'm getting a CEL. I brought the car in and the codes pulled. They were:

P0300 Random Misfire
P0306 Cylinder 6 Misfire
P0307 Cylinder 7 Misfire
P1141 Load O2 Implausible Value

I just purchased new spark plugs but haven't put them in yet. I figured I'd start there since I know they haven't been replaced in many years. I just thought it was coincidental that I get these codes right when I've had major service done. And you all are so knowledgable so......any thoughts?

RE: Misfiring codes creating a CEL
 

Coil packs are known to go on our cars....