Clutch Slipping After Only 40K Miles!

My clutch is slipping in 4th gear only 40K miles after replacement. I used the LUK kit that almost everyone here suggests. I have since learned that there are a few of those reporting issues with the LUK clutch and the Exedy kit is the GENUINE OEM replacement. I've since discussed this with LUK tech support and was told that at 180K miles, I should have also replaced the flywheel. I now have 220K miles and if I have to do it again, I'll try the Exedy kit. And although I have good power, the car seems to have that 'something's holding it back feeling' when I accelerate. My highway gas mileage is OK and performance at highway speeds remains stellar, but my all around mileage is off by a few MPG. I've done everything else that I can think of to alleviate the problem including regular maintenance:

- New Spark plugs
- Valve adjustment
- Timing belt job
- Cleaned the throttle body
- Replaced the PCV valve
- Replaced the air filter
- Changed the trans oil

The original clutch lasted 180K miles and I drive very conservatively. Might the clutch installation be at fault even though it ran fine for 10's of thousands of miles afterwards? Could LUK tech support be right about the flywheel being worn? What else am I missing?
.
.