Is Holley Terminator X worth $1,000 over a factory ECM and harness for an LS swap?

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

Computer and tune

• E67; LS2, LS3, LS376, LS7, LSX454; 2006+: Chevrolet Performance's LS control system guide specifies the kit is designed for LS crate engines with 58x crankshaft reluctor wheels, 4x camshaft timing, and electronic throttle control (generally 2006 and newer), and requires a fuel system holding a constant 400 kPa (60 psi) delivering at least 40 gph for LS2/LS3/LS376 or 50 gph for LSX454 and LS7. (Chevrolet Performance (via Scribd))

Transmission control

• Holley kit 550-916 supports 24x LS1/LS6 engines with EV1 injectors and includes electronic transmission control for 4L60E/4L80E with a transmission-control harness in the box. (Holley)
• In Holley's transmission software each upshift and downshift is independently configurable, but the upshift speed must remain above the corresponding downshift speed and the handheld rejects invalid overlap. (Documents)
• The Holley ECU prevents a downshift that would exceed the configured maximum RPM. (Documents)
• Holley part-throttle shift tables are based on throttle position versus speed, or on MAP versus speed in boosted calibrations. (Documents)
• Holley allows the wide-open-throttle shift RPM to be configured independently for each gear change. (Documents)
• Holley requires engine coolant above 122 degrees F and transmission fluid above 46 degrees F before it will apply the torque converter clutch. (Documents)
• For high-stall combinations Holley recommends 400 to 700 RPM or more between the TCC enable and disable RPM values. (Documents)
• Holley recommends unlocking most conventional lockup converters under moderate to hard acceleration, with a typical maximum TCC throttle-position value of 25 to 50 percent. (Documents)

Confirm against the instructions for your exact parts before wiring. More: Computer and tune in our tuning guide.