Just swapping in a TH350 for the 2 speed ST300 will be a night and day difference. The car will literally feel like it has 200 more HP. Mainly due to the lousy 1.76 ratio of 1st gear on the ST300. The TH350, being a 3 speed automatic, has about a 2.75 first gear. Regardless, an ST300, while super durable, and original, is a serious performance retarder. It's like running the 440 with your shoes tied together.
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Jeff 
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