The overdrive T5 ratios I've found are .63, .72, .73, .76, .86. So If you have a .63 od at 60 mpr with 28" tires and 3:73 rear your rpm would be 1834. 4th gear rpm would be 2925. Little high wouldn't you say. However for flat land Texas maybe ok. I'd be looking for a .72 od, that would give you 2106 rpm in 5th with little or no downshifting with the short hills in Texas.
