Your driveshaft count sounds awfully close to a 3.55 ratio.

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63 Valiant Wagon
225 - 4 bbl

yeah i used the gear calculator after looking at what rpm im at at 45mph in 4th which is ~1800rpms. Its saying 3.55.

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Old truck: 82 D150 225, 2bbl, dutra duals, 2.5" straight pipe to dual 2.5" tail pipes. Mud tires, 4spd, old forest service truck.
Current truck: 98.5 Ram 2500 ccsb, sport, 24v cummins, 5spd, 4.5" lift, 35's, 5" straight pipe.

Just push the car straight, one wheel revolution and have your sidekick count how many revolutions the driveshaft makes by eyeballling the primer spot, Its a pickup, there should be pretty good ground clearance to peer under there. Cleaner than taking the cover off.