I've got 3.73s in my stang and at 70 I'm at 2500 rpm and at 85-86 on the speedometer with a 21 tooth speedometer gear up from the stock 18 tooth. I think at 60 i'm a bit over 2000. (all in 5th of course) I'm not sure about the 60 cause I rarely run at that speed and don't pay much attention around there. The 23 tooth, which is recommended to correct the speedo, has too many teeth and doesn't mesh with the 8 tooth internal gear and gets chewed up in about a month. A 7 tooth internal is needed with the 21 tooth speedo to correct the 3.73s but unfortunately a 7 tooth internal is not made for the T45, only the T5 which will not work because of different splines on the gear.
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FOR SALE: 1996 Mustang GTS: 5-speed, K&N, removed air silencer, 3.73s, 48,000 miles. $11,500