Fuel filter?

I have taken adequate care of my Elantra, regular oil changes, transmission oil changes.

Last few months it seems like it has lost some power, sluggish and sometimes does not downshift smoothly while driving on an upgrade or accelerating.

The car shop replaced the fuel filter (without telling me first) for $175 then charged another $200 to change the Throttle position sensor. Since then, the RPM's race all over, car hesitates, hiccups, wants to cut while stopped at a light. When I start up first thing in the morning (cold engine) the RPM's can race to 4000. On idle the engine runs rough.

Took it back - shop said it might be a bad part. They said they changed it and the car ran ok for 3 days. Now the same problems are back. I told them I didnhave any of these problems BEFORE I took it in. They are giving me the run around and say they need to do "more tests."

I have no check engine light (CEL) warnings.

A friend said it might be the fuel filter or pump. He looked at the seat and there is no indication that it was removed - I understand that's the way to get to the fuel filter. I called the shop and asked how they changed the filter. The answer I got was "we didn't remove the seat or the gas tank. The fuel filter is outside the gas tank."

I don't know enough about my car to verify this. Does the Hyundai Elantra 2004 have a fuel filter OUTSIDE the gas tank?

Also, I am leery about taking my car to these guys again. Can you tell me what could be the problem if changing the TPS didn't help much?

thanks.