2007 GMC SIERRA 3500HD

Typical onset: 150,000-250,000 mi

Symptoms: white smoke on cold start, rough idle, fuel dilution in oil, eventual catastrophic loss of compression, metal shavings in oil pan

Fix: Failed injector tips overfuel the cylinder, washing down walls and cracking pistons. By the time you see symptoms, piston damage is often done. Requires complete engine teardown, new pistons, rings, bearings, injectors. 40-60 labor hours for full rebuild.

Estimated cost: $8,000-15,000

Typical onset: 80,000-150,000 mi

Symptoms: transmission fluid leaking near radiator, fluid in coolant or coolant in trans, transmission overheating, milky fluid on dipstick

Fix: Factory cooler lines corrode and leak or rupture internally, cross-contaminating coolant and ATF. Requires new cooler lines, often external cooler upgrade, full fluid flush of both systems. 4-6 hours labor, more if contamination caused internal trans damage.

Estimated cost: $800-2,500

Typical onset: 100,000-180,000 mi

Symptoms: clunk when shifting into gear, excessive drivetrain vibration, visible sagging of transmission tailshaft, harsh shifts under load

Fix: The rear transmission mount collapses from heavy towing loads. Simple replacement but requires supporting trans. 2-3 hours labor. Use heavy-duty aftermarket mount on trucks that tow regularly.

Estimated cost: $300-600

Typical onset: 120,000-200,000 mi

Symptoms: hard starting, low rail pressure codes (P0087), loss of power under load, metal contamination in fuel system

Fix: CP3 pump wears internally, metal debris circulates and damages injectors. Requires pump replacement plus often all 8 injectors if contamination spread. 10-14 hours labor for pump and injectors.

Estimated cost: $4,000-7,500

Typical onset: 90,000-140,000 mi

Symptoms: loss of coolant with no external leak, white smoke from exhaust, reduced power, P0401 code (EGR flow insufficient)

Fix: EGR cooler becomes clogged with soot or cracks internally, leaking coolant into exhaust. Replacement is straightforward but access is tight. Many delete the EGR entirely where legal. 5-7 hours labor for replacement.

Estimated cost: $1,200-2,000

Symptoms: coolant loss, white exhaust smoke, coolant in oil (milky), overheating under load, bubbling in overflow tank

Fix: Usually caused by untreated overheating event or bad head bolts. LBZ uses TTY bolts that stretch. Head gasket job requires machining heads, ARP studs recommended. 18-24 hours labor for both sides with studs.

Estimated cost: $3,500-6,000

Typical onset: 60,000-120,000 mi

Symptoms: fuel weeping from filter housing, air in fuel system, hard starting, low fuel pressure codes

Fix: Plastic fuel filter housing cracks at mounting tabs or water drain valve. Allows air intrusion. Replace with updated aluminum housing. 1-2 hours labor.

Estimated cost: $400-700