2020 GMC SIERRA 2500HD

Typical onset: 30,000-80,000 mi

Symptoms: sudden loss of power under load, severe rod knock or internal knocking, metal shavings in oil, check engine light with misfire codes, catastrophic failure while towing

Fix: Complete engine rebuild or replacement required. Rod bearings fail prematurely, wiping out crank journals and taking pistons with them. Typical job is 25-35 labor hours for short block swap or full rebuild with machine work. GM has issued TSBs but no recall; some warranty extensions on case-by-case basis.

Estimated cost: $12,000-18,000

Typical onset: 40,000-90,000 mi

Symptoms: transmission fluid in coolant (strawberry milkshake in reservoir), transmission overheating warnings, erratic shifting, coolant loss with no external leaks

Fix: Internal cooler in radiator fails, mixing ATF and coolant—requires radiator replacement, full trans fluid flush (multiple cycles), sometimes transmission rebuild if contamination caused internal damage. 6-10 hours labor depending on whether trans needs pulled for inspection.

Estimated cost: $1,800-4,500

Typical onset: 60,000-120,000 mi

Symptoms: reduced engine power message, DEF system fault codes (P20EE, P20B9), 'DEF range 100 miles' warning despite full tank, hard start in cold weather, check engine light

Fix: DEF tank heater element fails or lines crystallize from poor-quality fluid or infrequent use. Requires DEF tank removal (8-12 hours), heater replacement, injector cleaning or replacement, and sometimes SCR catalyst if contaminated. Use only top-tier DEF and avoid letting truck sit for weeks unused.

Estimated cost: $1,200-3,200

Typical onset: 50,000-100,000 mi

Symptoms: clunk when shifting from park to drive, vibration at idle in gear, excessive driveline movement under throttle, visible sagging or torn rubber on mount

Fix: Crossmember-style transmission mount tears or separates, especially on trucks used for heavy towing. 2-3 hours labor, straightforward replacement. Check during any trans service.

Estimated cost: $350-650

Symptoms: hard starting, loss of prime (long crank), fuel in valley under intake, rough idle and power loss, metal contamination in fuel system

Fix: Fuel filter housing can crack or leak at the head (2-3 hour fix, $400-800). The CP4.2 high-pressure pump, while less problematic than earlier CP4s, can still fail catastrophically and send metal through the entire fuel system, requiring tank drop, all injectors, lines, pumps—$10K+ job. Many owners install aftermarket CP3 conversion or Disaster Prevention Kit as insurance.

Estimated cost: $400-12,000

Typical onset: 20,000-60,000 mi

Symptoms: excessive oil consumption (1 qt per 1,000 mi or worse), blue smoke on startup or acceleration, loss of compression, misfires on multiple cylinders

Fix: Related to the catastrophic failures above—rings don't seal properly from factory or pistons score cylinder walls. Full teardown reveals damaged bores requiring sleeving or block replacement. 30+ hours labor. GM claims 'normal oil consumption' up to 1 qt per 2,000 mi, but many engines grenade before reaching that point.

Estimated cost: $8,000-15,000