Does a 2004 LS swap with a 99 Z28 gauge cluster need special tach wiring?

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

Tach and speedometer signals

• LS Control System kit: The brown bulkhead wire is an unscaled vehicle-speed output intended for auto-scaling speedometers. (Chevrolet Performance)
• Gen IV 58x (19201327 kit): The 19201327 kit's brown wire is an unscaled vehicle-speed output for auto-scaling speedometers. (Chevrolet Performance)
• The SGI-5E converts a 4,000 ppm transmission speed sensor or ECM output signal up to 8,000 ppm for an aftermarket speedometer. (Dakota Digital)
• PSI's black under-dash wire connects to the speedometer. (Performance Systems Integration)
• E38; LS2/LS3/Vortec 58x: The dark green/white bare wire is the ECM's calculated vehicle-speed output for the speedometer. (Current Performance Wiring)
• The Classic Instruments SN74Z module can condition either the tach or the speedometer signal, but not both at the same time. (MotorTrend)

Harness and power

• E38 ECM; Chevrolet Performance NA LS control kit 19171935; LS2/LS3/LS376/LS7/LSX454; 58x/4x; 2006+: Tach output is a 2-pulse-per-rev square wave. (Chevrolet Performance)
• 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: Underdash output wires: MIL, speedo, tach. (PSI Conversion)
• 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: Tach must be set to 4-cylinder mode; AutoMeters may need a resistor. (PSI Conversion)

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