A torque converter never locks up 100%. The physics of the stator almost doubling the engine torque just before the transmission input shaft begins to turn also causes the best possible RPM lockup to be 90%- - - -100 RPM in- - - -90 out. That's why modern torque converters in transmissions such as the 350C and 700R4, etc. use a single disc clutch inside the torque converter to eliminate the slip during light throttle cruise conditions. No matter what the stall speed is, there's no way to stop all the slip unless you use a locking converter. I'd recommend going back to the OEM converter for the 700R4 and installing the electrical controls to make use of the lockup clutch. It's a simple system which does not require a computer- - - -just a vacuum switch and a "brake on-off" (BOO) switch.
BTW- - - -the first transmission to use a locking converter was a 1949 Studebaker, followed shortly thereafter by the 1955 Packard Ultramatic. There's nothing new under the sun!
Jerry
