The year the shudder outlived its free fix — same transmission as the 2019, none of the coverage.

The pattern that makes this year Squawking rather than Chirping. One owner's eight-speed "completely deteriorated after 4 years and 64,000 miles, exactly after the powertrain warranty" — with no warning lights, only the shudder. Another had the transmission serviced and was told it was no good and about to fail, quoted $8,000. A third reports a defective torque converter at roughly 92,000 miles despite following the full maintenance schedule. GM's 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 what a converter can do to the rest of the unit. On a truck of this age the powertrain warranty is gone, so the shudder test drive is the whole inspection.

If the truck has the six-speed rather than the eight-speed, there is a genuinely valuable free programme attached to this model year. GM's Customer Satisfaction Program for 2020 trucks covers a slight deformation in the transmission's stator shaft, which the programme says causes vibration and a decrease in shift performance — and the stated remedy is that dealers replace the transmission. Not repair it, replace it, at no charge. Because the symptom is vibration, it is very easy to mistake for the eight-speed shudder and pay for a flush that was never going to help. Confirm which transmission the truck actually has first: ignition on with the engine off, shifter to L, press plus and count. If it stops at six, phone a dealer with the VIN.

A specific, diagnosable engine fault with a specific free fix. GM's Special Coverage for this model year covers the engine's bank 2 exhaust camshaft position actuator valve solenoid failing, which lights the check-engine lamp and sets a code — usually P0024. GM's wording is explicit: dealers replace the solenoid as necessary and the repairs will be made at no charge to the customer. Owners in this file hit it, one noting that GM had issued a bulletin to fix the part. Another reports code P0024 alongside a failing Apple CarPlay connection. No years-or-miles cap is stated in the programme summary, so none is claimed here — check it by VIN.

Recurring and cheap to catch. Owners report the check-engine light with the cooling fan running constantly and continuing for an extended period after the engine is switched off, traced to a thermostat that failed at under 50,000 miles. It is not a big bill by itself, but a truck that has been driven with a cooling fault for a while is a different proposition from one that has not. After your test drive, switch it off, stand next to it for a minute, and listen.

One owner at 54,250 miles reports a rear differential bearing going out — audible and felt as grinding at all speeds — alongside the transmission jerking between gears, and notes that either could cause an accident if it failed completely. GM's service literature for these years carries a procedure for replacing rear axle c-clips for a rear axle clunk, and separately an engineering bulletin asking technicians to report back on a loud bang or grinding noise from the rear axle area on 2015 through 2020 trucks. That last one is GM asking the field for information, which is its own signal. Drive it on a quiet road with the windows down and listen at the rear on and off throttle.

GM's Customer Satisfaction Program for a front differential housing built with a 12 mm hole in its top surface covers 2015 through 2022, so this year is in scope. If the hole is present, the dealer rebuilds the front axle with the correct housing at no charge. Given that this year's file also contains rear differential and driveline noise, it is worth having a dealer check both ends by VIN before you assume any noise from underneath is a paid repair.