My first CEL just came on lastnight car does weird thing...
 

So while driving to the movies my CEL came on...
I noticed that my Tachometer was off when i was going 60MPH and it was showing that car doing 1k RPM. When i pressed gas it went up to two and when i slammed on pedal it went to 3 and slowly to 4k RPM. It idles ok and no hesitation... So im really confused now.
I have a bad catalytic converter and im thinking that O2 sensor went bad but then im curious why would my tachometer would act up??? Anyone got any ideas???

Have the codes read and post them.