My 2002 Buick Regal with 3.8 engine has started limiting itself to 3900 - 4000 R.P.M., it will not upshift with wide open throttle. I want to find the problem so I want to change the fuel filter, but can find none. Any suggestions?

I doubt it's a fuel filter, usually you will get a check engine light with a lean code. If you haven't replaced it in 12,000mi it would be good to do anyways. I am not certain where it is on that car, check the firewall under the hood, check down by the gas tank, then check along the fuel line under the car, it should pop up some where.

It sounds like to me either an Air Filter is plugged (but not likely) or a possibility of a catalytic converter going out. A plugged cat will start by limiting the rpm, progressively getting worse then eventually lead to overheating of the engine while limiting the rpm typically under 3,000.

a 5 year old cat clogging up? i've never heard of one going bad that fast.