2001 GMC SIERRA 2500HD

Typical onset: 80,000-150,000 mi

Symptoms: White smoke on startup or acceleration, Rough idle and poor fuel economy, Fuel in coolant (dilution visible on oil dipstick), Hard starting when cold

Fix: Requires cab removal to access injectors properly, though some techs do it with cab on for rear cylinders only. All 8 injectors should be replaced as a set with updated parts. Budget 16-20 hours with cab off, 12-14 hours cab-on method but compromised access. Use OEM or quality reman injectors.

Estimated cost: $4,500-7,000

Typical onset: 120,000-200,000 mi

Symptoms: Excessive oil consumption (1 qt per 500-1,000 miles), Blue smoke on startup and under load, Loss of compression in one or more cylinders, Carbon buildup visible in tailpipe

Fix: Rings collapse or lose tension, often on cylinders 4, 6, or 8. Full engine rebuild or replacement required—no shortcuts. Pull engine, hone cylinders, replace all rings, bearings, and gaskets. 24-30 hours for complete rebuild. Some opt for reman long block to save time.

Estimated cost: $4,000-6,500

Typical onset: 60,000-120,000 mi

Symptoms: Transmission fluid leak at radiator or hard lines, Puddles of red ATF under truck, Low fluid level causes delayed shifts or slipping, Corrosion visible on steel lines at fittings

Fix: Factory steel lines rust through where they connect to radiator or at frame brackets. Replace both main cooler lines with stainless or upgraded rubber hose kit. Also inspect internal radiator trans cooler for cross-contamination. 2-4 hours depending on line routing and frame rust.

Estimated cost: $400-800

Typical onset: 100,000-180,000 mi

Symptoms: External coolant leaks at head/block joint, White smoke from exhaust, Overheating with no visible leaks, Coolant in oil (milky dipstick) or oil in coolant

Fix: Head gaskets fail between cylinders or into coolant jackets. Both heads must come off—don't do one side only. Resurface heads, replace gaskets, check for warpage. Use Fel-Pro or equivalent multi-layer steel gaskets. 14-18 hours labor. Often find cracked heads on high-mileage trucks.

Estimated cost: $2,200-3,800

Symptoms: Hard starting especially in cold weather, Fuel prime pump cracked or leaking, Air in fuel system causing surging or stalling, Visible fuel seepage at filter head

Fix: Factory filter housing is plastic and cracks from heat cycles and vibration. Replace with upgraded aluminum aftermarket housing or newer OEM design. Includes new filter and water separator. Bleed system properly. 1.5-2 hours.

Estimated cost: $400-700

Typical onset: 80,000-140,000 mi

Symptoms: Gear oil dripping from rear of transfer case, Low fluid causes grinding or delayed 4WD engagement, Visible oil on rear driveshaft yoke

Fix: NP263 or NP261 rear seal wears from driveshaft runout and age. Drop rear driveshaft, replace seal, check for yoke wear. Refill with correct Autotrac II fluid. 1.5-2 hours.

Estimated cost: $250-450

Typical onset: 80,000-120,000 mi

Symptoms: Clunking over bumps or turning, Loose steering feel or wander, Uneven tire wear on inside or outside edges, Play visible when prying on tire at 12 and 6 o'clock

Fix: Both uppers and lowers wear out, especially on trucks used for towing. Replace all four per axle, not individually. Some uppers require pressing, lowers are bolt-in on this generation. Alignment required after. 4-6 hours for both sides.

Estimated cost: $800-1,400