Todd G.

KNP is the auxiliary external transmission oil cooler. Transmission heat is what kills a towing drivetrain, and this is the code that says you got the cooler from the factory.

KC4 is an engine oil cooler — not the transmission cooler, which is KNP. How to find it on the truck, and why the two codes get confused constantly.

NZZ is GM’s off-road skid plate package. Usually bundled with Z71 — GM says so for 2016 — but it is its own code, and it is the one that proves the plates were fitted.

NQH is GM’s two-speed electronic Autotrac transfer case — the rotary dial with an AUTO mode. It is also the transfer case named in GM’s own Service 4WD bulletin.

GU5 is a 3.23 rear axle ratio — the tallest common gear GM puts in a full-size truck. Best empty-truck economy, worst tolerance for a tire upsize.

GU6 is a 3.42 rear axle ratio — the most common gear GM builds, and the one NHT lists. Why it became the default, and what it costs you on bigger tires.

GT4 is a 3.73 rear axle ratio — the working gear. Every record we hold, 2000 to 2026, says 3.73. What it does to cruise rpm, towing and bigger tires.

G80 is GM’s locking rear differential — but it has not meant the same hardware for fifty years. Positraction on a 1973 C10, an automatic locker on a 2026 Silverado. Here is every year we hold a GM document for.

NHT is GM’s Max Trailering Package. On 2021 trucks the factory documents put it at an 8,200 lb max-tow rating with a 9.76-inch rear axle.

Z82 is GM’s trailering package. The factory documents list a Class IV hitch and 11,000 lb capacity on 2016–2018 trucks — here is the full picture.