[TurboII]

Just found out about this site. Was hoping someone can help me with a few issues. 97 Tacoma regular cab, 2WD, 2.4L 4 cyl, 90K, 5 spd. Is in excellent condition(truck originally from TX). Bought in 03 w/ 60K. It is my second vehicle/winter car. Only put on about 5K a year on it. Drive it almost daily in the winter, but maybe a couple of times a week rest of the year. Drives great, and have had no problems with it. There are a few recent issues.
1. How much oil in the engine? Manual says 5.8 qts w/ filter. I have been using Fram filters. 5 qts fills above full on dipstick. Dealer told me to follow manual. Have been just putting in 5 qts. Have never understood this.
2. Check Engine light went on last fall. Code is P0420. Autozone said it was "Bnk 1 Cat". Said it could be bad spark plug. Anyone know how to diagnose/fix this?
3. Brake light goes on intermittedly.
4. It just started popping out of gear. First occasionly 5th, now occasionly 3rd too. Has always shifted like butter.
Sorry this post is so long. Wish I knew about this site earlier. Thanks again for everyone's help.