2015 Ram 2500, 6.7L Cummins, 68RFE, 94,000 miles. Mild economy tune added at 45,000 miles. Customer complaint: intermittent slip in 6th gear under load, occasional hard downshift from 6th to 4th when climbing grades. Truck had already been to three shops. Two quoted a full transmission replacement ($4,200–$4,800). One replaced the solenoid pack for $1,100 — no change in symptoms. When it came to me, I started with live data before touching anything. First observation: TFT at highway cruise was 247°F without a trailer. That's already high. Under simulated load on an uphill grade, it climbed to 271°F within eight minutes. The truck had no auxiliary cooler and the factory cooler was partially blocked with varnish — flow rate was well below spec.
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