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Either a SCT XCal 2, or a used Superchips Max Microtuner (Model 1725) if you can find one, would be a good investment since you have an automatic. A used flash tuner would save you some money and can do everything a new tuner of the same type can do. The chance of finding a used XCal 2 is slim since it's relatively new, and they cost more than $300, but they are much more versatile with respect to user performance adjustments than the Superchips tuner is.
I would have said that but there is supposedly only a very limited adjustability of transmission shift points/pressure with a Predator when used on a '98 model. That may be only a story, as I have no experience with using a Predator on a '98 automatic, but maybe someone on here has.