RPM calculator - what percent slip from lock-up converter?

[Derek69SS]

I've been playing with the RPM calculator on TCI's website to see if I think I'll be able to live with my 4.10 geared 12-bolt posi rear I just bought.

The trans is a '95 4L60E with lock-up converter, with (I believe) 0.7:1 ratio 4th gear.

How much do these slip on the highway at cruising speed? I would assume they don't actually "lock" like the name suggests, or do they?

I may just stick the old 3.08 10-bolt rear back in for the long trips, which will be easy since it has disc brakes (don't have to disconnect anything, and bleed them ), the speedo is programable, and I'll have an "extra" computer programmed for the similarly set-up LT1 in my wagon, which will be programmed for 3.08s also.