My 09 Acadia SLT started burning a lot of gas & took it to the shop.Gas problem?

What is your question?

Check engine light came on I took it in shop chgd, cat. converter, light still on, it started burning gas, went from 22 mpg to 15 mpg. The shop I took it too said it needed a TCM. Parts # PO989,PO877, POO089,PO301, @ P497..My vehicle has 168,000 miles, I have always been very punctual abt getting anything repaired. I was told the estimate to repair was 4764.21. I was stocked to say the lest..other than using more gas it runs fine. HELP PLEASE...

What makes this problem better or worse?

Nothing at this point, have not driven it anymore

How long has your 2009 GMC Acadia had this problem?

Few weeks