are well known to run lean, causing high combustion temps and high NOx. In turn, this causes cat and O2 sensor problems. It's all downhill from there.
Change your fuel filters every 12 months/12,000 miles and no more. Also, pouring in your favorite flavor of "mechanic in a bottle" does NOT get the injectors clean enough. You'll need to take them out and have them run through an ultrasonic back flusher. Reputable shops do this about $20 each and will send you a print out of before and after flow tests. OR you could buy the ~$2000 machine and DIY.