I take you are talking about when it goes into OD which is D. Is your car a highway driver (lower rpm torque) or high performance? You can use a formula to see rpms at a certain speed.

https://www.ringpinion.com/calculators/Calc_RPM.aspx

1:1 in 3rd gear - normally will not go into lockup

I think .7 in OD.

If you have lockup it will reduce about 200 rpm more at cruising speed - no acceleration.

If you do not want OD put shifter in 3rd. 1 to 1

Trans will run coolest in Lockup, but trans heat may not be a problem, with a trans cooler and how you drive the 56.

Last edited by 42465967; 04/27/2017 2:02 AM.
1959 GMC 100 Fleet
Follow in the DITY