The past couple of days, I had noticed by transmission shifting a little rougher than normal ('02 GC Limited 4.7, 80K miles). Yesterday the check engine light came on and I pulled these codes: P0138 and P0141, which are related to the O2 sensor, which I understand. However, I also got a P0735 - Gear 5 Incorrect Ratio 17119. The transmission is barely shifting rougher than normal; someone who hasn't driven it before probably woudn't even notice it. But as far as I can tell, fifth gear is fine. Where should I begin to diagnose this problem? (I hope I don't have to start worrying about rebuilding it!
Thanks for any advice!