Except he has an 8 tooth drive gear in that 91 AOD so the highest correct ratio he can do with the stock setup is 3.27s. And yes you will be off in your shifts if you don't have it setup right. Got to swap the drive gear from 8 tooth to 7 or 6 tooth to run a higher ratio than 3.27 and if someone mentions the 23 tooth gear I'm going to commit seppuku. The 23 tooth gear is NOT A FORD GEAR and will get chewed up in a Ford trans. Its a Chrysler mesh FYI.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.