I did the math and I think I had it right. With the T-56 a 3.73 gear equates to a 2.90(give or take a few). To get the right "feel" to the tires you would need atleast the 4.10 gear. That comes out to about 3.55 or so. the 4.30 comes out to 3.73 and 4.56 comes out to 4.10.
I certainly hope that's all it is that is making your pony so slow. I'll trade tranny's with ya if you want.
I could use the T-56 in the GT. Although, fisrt gear would be useless.
Oh well, hope this helps.
Later.