fesgali

A while back I had a problem where the car would struggle going 3k rpm at 50mph and got 19-20mpg .

I had the catalytic converter changed and the throttle felt great, got 26-27mpg and was excellent.

Over a period of 2 weeks i saw the mpg drop when calculating it each time i filled up to where it is now at 20mpg and sometimes hitting 22 if i'm lucky. Their has been no difference in driving styles when i was getting 26-27mpg and now. The engine is starting to slack again but it's not as bad as it was as i stated up top.

I've done seafoam and had no difference. Some guy at chevy said it could be the muffler as it sometimes goes after the cat dies.

Any ideas? 2000 v6 a4