Did you lower your fuel pressure when "tuning" it at the dyno? If so, you probably were running rich because of bad O2 sensors. When's the last time you replaced them? If you replaced them recently and your car runs better lean, you may want to get a custom chip burned.
The problem with twiddling with fuel pressure is that the computer will just compensate by changing injector pulse width. Read the article about Adaptive Strategy in Articles/Electronics on this site.
You could also try just resetting your computer at the track. This will clear any adaptation values. If you do tune at the dyno, you should reset the computer before every run, too. This will make every thing consistent from the dyno to the track.
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351W 89 Mustang GT Convertible