1989 chevy celebrity issue

Hi there, new to the forums...

Ok heres the problem.. I have a 89 celebrity with about 150,000 miles on it and seems to be running rich. I just did tune up on it which included spark plugs, wires, and new o2 sensor... Before i did all this tune up stuff it seem to start running rich and thats what made me think it needed a tune up... Also it the engince light would come on before the tune and does not anymore.. it only used to come on brifely if that means anything to anyone before the tune up.. This car i dont think has ever had a fuel filter replaced either so maybe its just not getting enough fuel.. Here is an example: when im at a traffic light and give it half throtle it will bog thur the gears but yet be smooth... just not running quite right.. Does anyone know what this could be brought on by...

Thanks brian