What does it take to keep my 4x4 transfer case and cable speedometer with an LS swap?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

• LS Control System kit: The ECM is programmed to expect 40 pulses per revolution from the VSS, typical of automatic transmissions. (Chevrolet Performance)
• LS Control System kit; 4L60 / 4L80: The LS Control System harness is designed to plug into the output speed sensor of 4L60 and 4L80 transmissions, which have a 40-pulse output. (Chevrolet Performance)
• late-model GM automatics: Late-model GM transmissions used an internal speed sensor outputting 128,000 pulses per mile. (Dakota Digital)
• The SEN-01-128 recreates the missing high-frequency rate when converting to an older transmission with a mechanical speedometer output. (Dakota Digital)
• TH350 / TH400 / 700R4 / 2004R: The SEN-01-128 fits GM transmissions with a 7/8-inch male-threaded speedometer cable outlet, including TH350, TH400, 700R4, and 2004R. (Dakota Digital)
• The SEN-01-128's 128,000 pulse-per-mile sine-wave output is a direct replacement for the stock GM internal speed sensor, letting the ECM receive the signals it needs. (Dakota Digital)
• Sources differ: Conflicts with the current SEN-01-128 manual, which states the product is NOT for use with transmission shift computers or ABS systems and that its non-calibrated output may cause issues.

Confirm against the instructions for your exact parts before wiring. More: Tach and speedometer signals in our tuning guide.