Kent1979

Hi
I have a high ltft problem on my 350CGI its reading +22 on bank1 and +17 on bank2 stft is hovering around 0 +-10.
My journey so far:
had the car for 800km before the the timingchain needed to be changed (done at stealership) balancesprocket inspectet and it was ok.
when i drive spirited it smells rotten...
I´ve passed a buddy on freeway at high speed with pedal mashed and he said it was smoking black...
stft does not go negative when high revs.
i have tried testing leaks with water and propane no luck.
Changed maf sensor... no change
Changed both upstream and both downstream o2 sensor and no change
All old o2 sensors did have some black sod as in rich mixture.
black deposits inside tailpipe.

I think its overfueling, but i cant figure out why its trimming so much positive..

Any test?
Any checks?
Any thoughts?

I can live with bad fuel economy, but i dont want to throw 4 new cats at it!!

PLEASE HELP ME