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If it is a Standard 4-Speed Transmission, fourth gear is Direct, no different than Third Gear in a 3-Speed manual transmission, or Drive, Third Gear in a 727 or 904 Torqueflite.

You would need a an Overdrive Transmission to bring the RPM down at freeway speeds. Higher continuous RPM does accelerate engine wear, though you may be able to live with that.

Swapping to Taller tires works similar to swapping in, say, 3.54 or 3.23 rear axle gear ratio, but off-the-line performance would suffer a bit as well.

There are lots of great Gear Ratio calculator applications available, wherein you input rear-axle ratio, transmission ratio (1-to-1 in high gear for a Standard, non-overdrive transmission) along with Tire Diameter which will calculate Engine RPM based on Speed in MPH.

You can run the numbers to determine what combination would produce your desired results, though it is always a compromise.



904, with TF-2 kit, 2800 stall.
Moved away from 3.23s a while ago, so the 91's are here to stay.

2016 Ram 1500 Crew Cab: 5.7, 65RFE, 4.56 gears with locker, Hemifever tuned, AFE intake, 87mm throttle body, JBA headers, 3" Flowmaster exhaust, split to dual 2.5" exits. 13.57 best ET so far.

Searching for new A or B Body Project!