1991 DODGE D250

Typical onset: 100,000-180,000 mi

Symptoms: Slipping under load, especially in overdrive (A518), Delayed engagement into Drive or Reverse, Burnt transmission fluid smell, dark/metallic debris on dipstick, Loss of 2nd or 3rd gear — limp mode or manual-shift-only operation

Fix: The Cummins torque murders stock A727/A518 units. Rebuild with upgraded clutches, bands, and valve body takes 12-16 hours; many owners opt for aftermarket converters and shift kits during rebuild. Transmission oil cooler often gets clogged and contributes to early failure — replace cooler as preventive if original.

Estimated cost: $2,200-3,800

Typical onset: 80,000-150,000 mi

Symptoms: Sudden catastrophic loss of power, white smoke, Engine cranks but will not start after running fine moments before, Metal debris in oil pan on inspection, Timing case cover damage or cracking visible externally

Fix: The dowel pin that locates the gear housing can back out and drop into timing gears, grenading the front case and sometimes cracking the block. If caught early (noise, vibration), pull front cover and stake/Loctite the pin — 6-8 hours. If it lets go, you're looking at new timing cover, gears, possibly injector pump drive, and block repair/replacement — 20-30 hours labor plus machine work. This is why many Cummins guys do the 'KDP fix' preventively.

Estimated cost: $400-800 (preventive) / $3,500-6,500+ (after failure)

Typical onset: 90,000-140,000 mi

Symptoms: Hard starting, especially when warm or after sitting, Surging or hesitation under light throttle cruise, Loss of power uphill or under load, Injection pump whine or premature wear (starved for fuel)

Fix: The mechanical lift pump on the Cummins block is weak from the factory and wears out. Replacement takes 1-2 hours and is straightforward, but many owners add an aftermarket electric lift pump in-line to protect the expensive injection pump. Check fuel pressure at the injection pump inlet — should see 15-20 psi; less than 10 psi means pump is dying.

Estimated cost: $150-350

Typical onset: 120,000-180,000 mi

Symptoms: Heavy rod knock on cold start, fades slightly when warm, Low oil pressure at idle (under 10 psi hot), Metal flakes or bearing material on oil drain plug magnet, White smoke or coolant consumption if head gaskets also failing

Fix: The LA-series 5.9L gas engine wears main and rod bearings, especially in trucks used for towing. Often see head gasket leaks at same mileage due to head warping from overheating. In-frame bearing replacement is 18-22 hours; many owners go straight to reman short block or junkyard swap given the labor involved. Head gasket job alone is 8-10 hours and often uncovers deeper issues.

Estimated cost: $2,800-4,500 (bearings + gaskets) / $3,500-5,500 (short block)

Symptoms: Long horizontal cracks across top of dash pad, above instrument cluster, Crumbling foam backing on underside if dash is removed, Sun damage especially in southern climates

Fix: Not mechanical, but universal on these trucks. Dash pad cracks from UV exposure. Replacement dash caps or covers run $100-300; full dash replacement is 4-6 hours labor and requires removing steering column and instrument cluster. Most owners live with it or use a cover.

Estimated cost: $100-300 (cover) / $600-1,200 (replacement)

Typical onset: 80,000-150,000 mi

Symptoms: Clunk or thud when shifting from Park to Drive, Excessive vibration at idle in gear, Visible sag or tearing in rubber mount under transmission crossmember

Fix: The transmission mount takes a beating from Cummins torque and heavy payloads. Rubber tears and mount collapses, letting the transmission drop and stress the driveline. Replacement is straightforward — 1-2 hours with trans supported on a jack. Often done with engine mounts at same time.

Estimated cost: $120-250