OK, now for an opposing point of view. these guys are absolutely right, 3.73 or 4.10's are not any more prone to beakage than the stock 3.27s , however, if this is a stick car ford put a pretty stiff first gear in that tranny, so much so that most stock GT's would run (about) 13.7-14.10 depending on altitude, tune, etc, etc. When you put in a 3.73 or 4.10 then first gear lasts about 3 feet. that's great for the drags, but maybe not so cool for the street, especially if you drive in traffic. IMO I'd run no taller than 3.55's. And BTW I had a street car with 5.13's at one point, so I've been down this road many times. Try to find someone who has this mod and drive their car first. One more thing, nothing, absolutely nothing will improve performance better than a set of gears (as long as you can hook up) so if acceleration is your bag, then go for it.