What parts and wiring do I need to swap a 4L80E in place of a 4L60E in a GMT800 truck?

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

• The Quick 4 kit includes both the early large and late small output-speed-sensor harnesses, with black and purple wires terminating in the controller's white TSS connector. (US Shift)
• For 4L80E installations the Quick 1 manual says to connect the solenoid and TSS cables keyed correctly, connecting both TSS cables according to their labels. (US Shift)
• For 1999-2007 Gen III truck/LS-style harnesses, the 4L60E-to-4L80E conversion guide moves the transmission-connector brown wire from cavity U to cavity S, and repurposes the removed white wire (cavity S) and tan/black wire (cavity T) for the 4L80E input-speed sensor. (Uploads)

Confirm against the instructions for your exact parts before wiring. More: Transmission control in our tuning guide.