The best thing to do is take the car to a dyno and see where your powerband is. You should be able to better gauge what gears to get from that info.
Did you get your chip reprogrammed after the changes? If not, that may be a big part of it. If it's optimized for car the way it was and not the way it is now, you could be losing a lot of power.
What do you think of your Corbeau seats? Are they fixed or can they recline? Do you have pictures? At some point I really need to buy new seats. E-mail me so we don't disrupt this thread if you don't mind. Thanks.
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351W 89 Mustang GT Convertible