The eight-speed arrives, and so does the shudder — but this is one of only three years GM will flush the fluid for free.

The reason to take the shudder seriously is what sits behind it. GM's own service literature for these years includes a procedure to replace the torque converter and inspect the front pump and the transmission control module for metal — which is a polite way of saying the converter can shed material into the rest of the unit. In the complaint file, one 2017 owner had the fluid and the torque converter replaced by the selling dealer and had the problem return; another's transmission "locked up while I was on the freeway and refused to go over 40 mph"; another was told the whole unit needed replacing. The owner who published his invoice puts it well: don't drive a long time with it, because it is not guaranteed you won't need a torque converter or the transmission itself. A truck with a documented flush in its history is worth real money over one without.

The one federal safety recall on this year, and it is a serious one. The high-pressure fuel pump can come away from its mounting flange and damage the high-pressure fuel line; NHTSA's own consequence line is that a damaged fuel line can create a fuel leak, increasing the risk of a fire. Dealers replace the pump and the pipe free. The campaign covers 2016, 2017 and 2018 Colorados among nine GM nameplates. Confirm it shows completed by VIN.

A 2017 owner in the complaint file reports the oil-cooler line failing twice in two years on a truck with 50,000 miles, both times while driving, both times with alarms telling him to shut the engine off. GM has a Customer Satisfaction Program — its free-repair programme short of a recall — for exactly this on the 3.6L LGZ engine: high oil pump pressure in cold-weather starts can fail the engine oil cooler, its lines, or the pump itself, and GM's own wording is that if you keep driving with low oil despite the warnings, the engine may seize, causing a stall or loss of propulsion. The catch is the geography. The programme applies only to trucks in Canada or currently or previously registered in Alaska. Everywhere else the same failure is on the owner. Treat an oil-pressure warning on a cold morning as an immediate stop.

A genuinely alarming one, handled by GM as a satisfaction programme rather than a recall. If the transfer case actuator's motor brake sticks open, and the truck is parked in 4LO, on a slope of less than two degrees, with the system warm, and you switch the ignition off, GM says there is potential for the vehicle to roll back because the range fork can slip into neutral. The tell is code C0326 58 and a "Service AWD" message. Dealers replace the transfer case actuator assembly free. Separately, a Service Update covers trucks built with the wrong rear axle assembly, which GM says can cause unintended deceleration or lock-up at low speed when shifting into four-wheel drive, plus an incorrect odometer reading. Both are VIN checks.

GM documented that on certain 2017 to 2019 trucks, some kinds of off-road use can, in rare cases, set off the roof-rail airbags and the seat-belt pretensioners. The fix is a free reprogramme of the sensing and diagnostic module — the crash-sensing computer — with updated software. If you are looking at a Z71, or any truck that has clearly been used off pavement, this is the single most relevant free item on the list, and it is worth confirming the airbags have never actually gone off.

A nuisance that turns into a bill. Owners report the shifter or the park-position sensing failing to register park, so the ignition will not rotate far enough to release the key and the truck sits in accessory mode. The usual repair is a new shifter assembly, and owners note pointedly that it is not covered by the powertrain warranty. This pattern runs the whole of this generation and peaks on the 2022. Test it several times: park, switch off, remove the key, restart, repeat.

Two quiet GM programmes land here. The front differential housing may have been made with a 12 mm hole in its top surface; if it is there, the dealer rebuilds the front axle with the correct housing at no charge, and the programme's scope runs 2015 through 2022. And a missing rear axle shaft c-clip causes brake squeal from the rear, brake pulsation, and accelerated pad and rotor wear. Both are VIN-gated and cost nothing but a call.