99 Sonata Hesitation

Not sure how much info to give and still stay brief.

Bought about 1 year ago. Had check engine light: Code was for bank 1 lean.

Car ran fine. Reset light - stayed out for a day or two.

Several months later performance began deteriorating until car choked out and died

eventually replaced catalytic converter; much improved but some hesitation

hesitation continues especailly when cold; when was car has trouble upshifting

and is especially unresponsive around 2000 rpm

If I floor is it will shift but when I let speed/rpm drop to 2000 or so it wants to bog down.

Someone has suggested O2 sensors.

HELP!!!!

Thanks in advance.