The 2021 Ram 3500 with the 6.7L Cummins is a workhorse diesel that's largely bulletproof on the engine side, but the 68RFE automatic transmission and its supporting systems are the Achilles heel — expect mounting issues, cooler failures, and solenoid problems as miles pile on.
Transmission Mount Failure
Common · medium severity
Typical onset: 40,000-80,000 mi
Symptoms: Clunking on acceleration or deceleration, Excessive driveline vibration, Visible sagging or torn rubber on mount, Transmission shifts feel harsher
Fix: Replace transmission mount and crossmember bushings. Usually 2-3 hours labor with transmission support required. OEM mounts last longer than aftermarket — don't cheap out.
Estimated cost: $400-700
Transmission Oil Cooler Line Leaks and Cooler Failure
Common · high severity
Typical onset: 60,000-120,000 mi
Symptoms: Transmission fluid pooling under truck, Pink/red fluid dripping from radiator area, Overheating transmission temps, Burnt transmission fluid smell
Fix: Cooler lines corrode at fittings or cooler itself cracks internally. Requires cooler replacement and line replacement, plus full fluid flush. 4-6 hours labor. If coolant mixes with ATF, you're looking at a full transmission rebuild.
Symptoms: Harsh or delayed shifts, Transmission slipping between gears, Check engine light with P0750-P0770 codes, Limp mode activation, Won't upshift past 3rd or 4th gear
Fix: Solenoid pack lives inside the valve body. Pan drops, valve body removal, solenoid replacement. 6-8 hours labor. Should replace transmission filter and fluid simultaneously. Use OEM Mopar solenoids — aftermarket causes repeat failures.
Estimated cost: $1,200-2,200
Torque Converter Shudder and Lockup Clutch Failure
Occasional · medium severity
Typical onset: 70,000-110,000 mi
Symptoms: Vibration at 40-50 mph during light acceleration, Shudder feels like driving over rumble strips, Slipping on highway acceleration, Transmission overheating
Fix: Torque converter lockup clutch wears or fluid contamination causes shudder. Requires transmission removal and converter replacement. 10-14 hours labor. If caught early, sometimes a fluid and filter change with Mopar additive buys time, but converter replacement is inevitable.
Estimated cost: $2,500-4,000
Overdrive Solenoid and Governor Pressure Issues
Occasional · medium severity
Typical onset: 90,000-150,000 mi
Symptoms: No overdrive — stuck in 4th gear, RPMs stay high on highway, P0871 or P0845 trouble codes, Erratic shift points
Fix: Overdrive solenoid or governor pressure solenoid fails. Valve body removal required. 5-7 hours labor. Often combined with full solenoid pack refresh if one has failed.
Estimated cost: $900-1,600
Fuel Filter Head Leaks and Water-in-Fuel Sensor Corrosion
Common · low severity
Typical onset: 50,000-100,000 mi
Symptoms: Fuel smell near driver-side frame rail, Visible diesel weeping from filter housing, Water-in-fuel warning light intermittent or stuck on, Hard starting in cold weather
Fix: Filter head O-rings degrade or water sensor corrodes. Replace fuel filter assembly and O-rings. 1-2 hours labor. Use OEM Mopar filters — aftermarket heads crack.
Estimated cost: $250-450
Owner tips
Change transmission fluid and filter every 60,000 miles — the 68RFE does NOT have lifetime fluid despite what the manual says
Use Mopar ATF+4 only; other fluids cause valve body sticking and solenoid issues
Install an aftermarket transmission temp gauge — factory gauge doesn't warn until it's too late
Replace fuel filters every 15,000 miles and drain the water separator monthly if you use biodiesel blends
Inspect transmission cooler lines annually for corrosion — they rot from the inside out
Buy the Cummins, budget for the transmission — it's a $50k+ truck that needs a $2k transmission refresh every 100k miles, but the engine will outlast two transmissions if maintained.
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.
Fitment notes: High output AGM required for diesel; dual battery system on some configurations
As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.
Control Modules — 2021 Dodge Ram 3500
Every control module on the 2018-2023 Dodge Ram 3500 — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
Electric Power Steering Module (EPS)2.5 hr R&Rsecurity gateway +0.8 hr▸ programming details
📍 Integrated with steering column assembly, below instrument panel
🔧 wiTECH 2.0 or Autel MaxiSys Elite/Ultra
⚠️ Requires steering angle sensor calibration and end-stop learning procedure after replacement.
⚠️ Critical security module. Enforces Security Gateway protocol. Replacement requires dealer-level authentication and all modules may need reconfiguration.
Door Module (DDM/PDM)1.2 hr R&Raftermarket tool +0.3 hrwith power windows/locks▸ programming details
📍 Inside door panel, driver and passenger doors
🔧 Autel MaxiSys or wiTECH 2.0
⚠️ Controls window, lock, and mirror functions. Requires window auto-up/down relearn after replacement.
⚠️ Monitors DEF quality and level. Requires system reset after replacement.
Seat Control Module (SCM)0.8 hr R&Rrelearn only +0.2 hrwith power seats and memory▸ programming details
📍 Under driver and passenger seats
🔧 Scan tool with bi-directional control
⚠️ Controls seat position, heating, ventilation, and memory. Requires memory position relearn after replacement.
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2021 Dodge Ram 3500 6.7L I6 Cummins Diesel and can vary by trim.
🔧 Built by master technician Chris Hackleman · Master Technician · 20+ years.