I don't know yet , but I will be taking suggestions.
I will try my best to kill the first person who suggests SSEi or Bonneville!

Well, it'* not a girl, so Bonnie is out anyway.

I can't think of anything original. I'm out of beer. I'll have to get back to you. Enjoy it, bud. They can be a PITA sometimes, but they're an absolute joy. Even girls

What would I tinker with, I had my O2 sensor replaced when I first bought it, but where I bought it from the mech. there I don't think he'* very good, he'* foren. Also how many O2 sensors does my car have cause the bill for parts was like 60 some dollars. I had it fixed there cause he did it for free, from my check enging light.

OBDII cars have two O2 sensors per cat and at least one of them is heated. They are not cheap at all.

cheapest i find them for is 70.00 (AC Delco)

That sounds about right. The prices I have seen for various domestic OBDII cars ranges from 60-80 dollars.

I changed the filter. The gas mileage improve to 25 to 26 MPG with a fram filter. If the O2s are bad won't I get a service engine soon light?

500,000.00 cars are unpredictable, maybe it will maybe it won't . But for your milage sake , you should change them anyway!

With a bad O2, you won't necessarily get a SES light. The O2'* are cheaper thru www.gmpartsdirect.com. I think they're under $50.

O2 sensors just get tired over time, and cause you to run a bit rich. That'* where the mileage goes. I'm not saying this is your problem, but I AM saying this is one of the first things you need to look at if you know your sensor(*) are older than 50k or so.