If you have a 3.73 gear now, a 4.56 gear w/38's will achieve roughly the same RPM per MPH as stock.
If you have a 4.10 gear now, a 5.13 gear w/38's will achieve roughly the same RPM per MPH as stock.
A 4.88 gear w/38's will yield roughly the same RPM per MPH as a 3.96 gear ratio on stock tires, and is probably the best combination of pulling and economy. Of course, economy is a relative term as the mass of the rotating assembly is about to be triple or more. Certainly not good for stop & go driving.
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