Engine still lagging/bucking, help! Options

[GriffGirl]

I'm still having weird engine issues. It was bucking really bad until warm up, especially in higher RPMs. I did a tune-up which helped but didn't solve it, engine would still buck while cold at higher RPMs (3000+), and at about 3500+ when warmed up. Fiddled around some more this weekend, resulting in amazing improvement; now instead of bucking, it just kind of feels like it's dragging like a dog scraping its butt on the carpet. Yes, at higher RMPs, and regardless of what gear I'm in. I've done the following thusfar to resolve this issue:

•replaced thermostat
•replaced engine temp sensor
•replaced plugs, cap & rotor, air filter (improvement #1)
•replaced fuel filter
•seafoam gas treatment, seafoam vacuum line (discovered leak in gasket around header pipes)
•removed intake housing, cleaned the hell out of throttle body/plate
•realized that did nothing, REMOVED throttle body, discovered diamond mine in carbon deposits, cleaned thoroughly including all those tiny little vacuum tentacles
•whatever that thing is called (is it just the intake?) that the throttle body is attached to, well I sprayed the HELL out of it and soaked a rag too and did my best to clean it out. It looked like a stalactite cavern. Result was a marked increase in throttle response, made my car feel young again.

But still dragging ass on 3000+ RPMs regardless of gear. What is that thing the throttle body attaches to? Should I attempt to remove the cover from it so I can get rid of the rest of all that carbon build up? Is that my problem? Does anyone have any other ideas? PLEASE?

Thanks...

[GriffGirl]

I had no idea there was a fuel filter in the gas tank. Where the hell is it and how do I get to it? And why haven't I ever heard of it before!? But yes, I did change the one under the hood. (Boy that sucked. The bottom nut was really really tight.)

I'll try the thing with the vacuum lines, it certainly can't hurt. I did spray the ports that are on the throttle body though, I even discovered that if not careful, you can actually shoot that tiny straw INTO your intake manifold. Luckily I have small hands, a small flashlight, long needle nose pliers and a bit of luck.

As for the cat, I didn't even think of that. It too could cause my car to run pretty crappy, couldn't it? Is that something I can have a muffler shop do a back-pressure test for? I know a very good shop nearby who might be willing to do that. Is it worth checking into?