LSdominator

1998 TA Stock Ls1 w/six speed. Trying to achieve a stock tune! the initial dyno results were 294.7 HP at the wheels and it said my AFR's were in the low 14's which is dangerously LEAN so we tried changing the timing and adding fuel but it would not tune at ALL! I also dont know if the previous owner had it tuned before me or anything of that sort so that is a downfall to this situation...So I have a few questions.. 1) I have no knowledge of the 1998 Trans Am's being able to support a plug and play DLC tuner ( I just know of flash tunes for this year) so does anyone know if the 1998 Ls1 ECM allows the use of DLC tuners? 2) Could bad cats and oxygen sensors prevent it form being able to properly tune? 3) We didnt mess with the long term fuel trims so could the LTFT's maybe trip the computer to go back to stock parameters at a certian RPM preventing it from holding the tune? and Would the LTFT's need to be changed if so?
((We used an HP tuner))

I live in Colorado so idk if the altitude as any affect as well!
Thanks