This harness allows for a 6l80/90 to be put behind a GMPP crate engine and harness. Tap shift is made simple by provided up/down switch (we also include instructions on how to source your own switch if you prefer). HPtuners is required for install/tuning. Full diagnostic and tuning supported by most tools like HP Tuners – making tuning a breeze vs a separate aftermarket controller! Seamless operation with your GMPP harness.