The 1991 K10 with the 5.7L 350 is a durable workhorse, but the TBI fuel system, 4L60/700R4 transmission, and intake manifold gaskets are known weak points that require attention as mileage climbs past 100K.
Intake Manifold Gasket Failure
Common · medium severityTypical onset: 80,000-150,000 mi
Symptoms: Coolant loss with no visible external leaks, White smoke from exhaust on cold start, Rough idle and potential misfire codes, Oil contamination showing milky appearance
Fix: Replace intake manifold gaskets, often includes new distributor O-ring and coolant flush. 4-6 labor hours. Common to find corroded bolt holes requiring thread repair.
Estimated cost: $600-1,200
4L60/700R4 Transmission Failure
Common · high severityTypical onset: 120,000-180,000 mi
Symptoms: Slipping or delayed engagement, especially 2nd-3rd shift, No 4th gear/overdrive, Harsh shifts or complete loss of forward gears, Metal shavings in transmission pan
Fix: Rebuild or replacement required. Governor pressure issues and clutch pack wear are typical culprits. Rebuild takes 8-12 hours, replacement 4-6 hours. Oil cooler replacement mandatory to prevent repeat failure.
Estimated cost: $1,800-3,200
TBI Fuel Injector Clogging and Fuel Pressure Regulator Leaks
Common · medium severityTypical onset: 100,000-200,000 mi
Symptoms: Hard starting when engine is hot, Rough idle and stumbling on acceleration, Black smoke from exhaust indicating rich condition, Fuel smell in engine bay or visible fuel leaking from TBI
Fix: Clean or replace TBI injectors, replace fuel pressure regulator if leaking into intake. 2-3 labor hours. Often includes new fuel filter and pressure test.
Estimated cost: $300-700
Distributor Cap, Rotor, and Ignition Module Failure
Occasional · high severityTypical onset: 60,000-120,000 mi
Symptoms: Intermittent no-start, especially when hot, Random stalling while driving, Rough running and backfiring, Corroded terminals visible inside distributor cap
Fix: Replace cap, rotor, and if no-start persists, the ignition module mounted on distributor. Module failure common in high heat. 1-2 labor hours for complete distributor service.
Estimated cost: $200-500
Front Differential and Transfer Case Seal Leaks
Common · low severityTypical onset: 80,000-150,000 mi
Symptoms: Gear oil spots under front of truck, Low fluid levels discovered during service, Whining noise from front differential under load, Transfer case puddles near transmission
Fix: Replace axle seals or transfer case output seals. Front diff requires axle removal, 3-4 hours. Transfer case rear seal 2-3 hours. Check for worn bushings causing seal damage.
Estimated cost: $400-900
Fuel Tank and Sending Unit Corrosion
Occasional · medium severitySymptoms: Inaccurate or non-functioning fuel gauge, Fuel smell around tank area, Visible rust perforation on tank exterior, Fuel pump failure due to contaminated fuel
Fix: Replace fuel tank and/or sending unit. Corrosion accelerated by road salt and moisture. Tank removal 3-4 hours. Consider fuel pump replacement at same time if original.
Estimated cost: $500-1,100
Steering Gearbox Wear and Pitman Arm Looseness
Common · medium severityTypical onset: 100,000-180,000 mi
Symptoms: Excessive play in steering wheel, 2+ inches of free play, Wandering on highway requiring constant correction, Clunking noise when turning from center, Power steering fluid leaks from gearbox seals
Fix: Rebuild or replace steering gearbox, inspect and replace pitman arm and idler arm if worn. 3-5 hours labor. Alignment required after.
Estimated cost: $600-1,400
Buy it if the transmission shifts clean and doesn't leak — these trucks run forever with basic maintenance, but a bad transmission or ignored intake gaskets will cost you dearly.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.