Hello everyone! I am new here but here's my problem, I am working on a 2009 suburban 5.3l and it has 2 rich codes and my LTFT'S are through the roof, it is completely original nothing has been done to it other than an engine swap by a mechanic with a bad reputation (BTW I am a mechanic and this is my uncle's vehicle) and he needs his vehicle back asap so any suggestions would be appreciated, thanks!

Btw if it was a vacuum leak wouldn't i get a vacuum leak code?