Need help solving 61 drivetrain / RPM problem

[markeb01]

I haven’t taken the time to calculate the math, but a couple of points to consider – most vintage automatic transmissions will lose up to several hundred rpms in the torque converter. A Powerglide isn’t a stick shift, so there could be 400-500 rpms going to waste before the output shaft actually turns the driveshaft.

The other issue is how low to go in final drive rpms with an older, smaller engine. Dropping the rpms too far will leave you with a dog on acceleration. The engine needs to be operating in its torque range to move the truck most efficiently. New vehicles can propel a vehicle at highway speeds using very little engine rpm because they were designed that way. Our trucks were not.

And if the numbers provided were in fact counted by your mechanic (44/13), you do indeed have a 3.38.