Okay, then perform the tune up and see how it feels. I can have plenty of fun with a stock L24, let alone an L28. The things that make the biggest differences in driveability are not engine-related, IMO. First thing I'd do is a 3.9 or numerically higher rear diff and a late ZX 5-speed. Those changes wake the car up, more than bolting in little bits to the engine, especially if it's stock EFI. Tires are also on the list of things that completely transform the car. Invest in those things first, after a tune-up. Refer to Braap's fairly comprehensive post on modifying an engine with stock EFI: http://forums.hybridz.org/index.php/topic/95316-braaps-l6-efi-induction-advice-and-tips/