My N/A was getting horrible milage until I replaced the cat. Doesn't sound like your problem, though...

I'd suggest a tune-up, too.

well the PCV valve was replaced when i got the new upper, the new upper came with a new PCV valve surprisingly enough, and we replaced the plugs as well, wires are still on there though, but wouldnt it be running crappy if they were bad? i dont think anything having to do with the fuel pump, filter, or fuel pressure because its definetely getting fuel. here is my typcial day of driving to work:

5-6 miles of hilly gravel road, speed between 25-30mph, frequent revving between idle speed and 2500 at most

2 miles of curvy backroad, speed limit is 55...i usually accelerate onto to it mildly between 3k and 3500...then i put it in OD and run about 65 on it..

15 miles of open highway, speed limit 65, i mildly accelerate again up to about 70mph, set the cruise with AC, btw AC is on the whole time on the other ones..usually the revs stay right at 2k or a little over, i might pass 3 or 4 people at most and maybe go WOT one of those times.

rinse and repeat on the way home, done 5 times a week.

how much is a new o2 sensor? and how much is the special tool to change it? or is it even necessary...can a good mechanic tell me if its working properly or not? arent there two o2 sensors?

There are two O2 sensors. One behind the cat, and one before it. The one you need to be concerned about is the one in front of it. It'* visible by looking straight down, from above the engine, on the back side. It'* by the firewall and is bolted into your exhaust manifold down pipe.

New from GM they're about $65. I would suggest starting there since you don't know how old it is. I replaced mine on the 99 at 105K and I got 3-4 more MPG out of it. It was the original. They get lazy overtime, but won't necessarily throw a code.

As for the special tool... Go to your local AutoZone and ask to rent the O2 sensor removal tool. It'* basically a socket with a slit in the side of the case to allow for the wire to hang out. It'* very handy and makes the job SO much easier!

I get 14-17 stop and go

25-33 freeway

Stop and go is pretty bad

Your commute is less than desirable for fuel mileage. Consider an O2 and hope for the best.

Well I get 28.5 on the hwy, with my heavy foot! Extremely heavy 80mph in 65 zones! (only when truckers upset me happens sometimes) I try only to 7mph or so over! And in town with my heavy foot for accleration I see oh maybe 17-19 depending on how late I am! I know I need to slow down, my wife told me getting the Bonnie SLE was only going to encourage me and fast and spirited driving! Oh well I liked the thoughts of that! Cat converter? Air Filter, Fuel Filter or just a good old tune up might help your Bonneville SE!