40K Transmission Cooler Kit for Tru-Cool LPD47391

Brazed aluminum stacked-plate transmission cooler rated to 40,000 GVW, built as a direct replacement for the Tru-Cool Max LPD47391 (also sold as 47391). It ships as a kit — cooler, high-flow fittings, mounting brackets, hardware and hose clamps — so it goes in as a bolt-on auxiliary cooler rather than a bare core you still have to find plumbing for.

The core uses a low pressure drop plate design. That is the part worth understanding: a tightly packed fin-and-tube cooler will shed heat, but it also chokes flow, and on a cold morning a restricted cooler is what starves the converter and the rear lube circuit until the fluid thins out. The LPD plate stack keeps flow up through the whole temperature range, so it warms quickly in winter and still dumps heat when you are dragging a trailer up a grade in July. Two flange ports, machined finish, and the plate stack is stiff enough to take road debris and vibration without splitting a seam.

Mount it ahead of the A/C condenser in clean airflow and plumb it in series after the factory cooler, not instead of it, unless you are deleting a failed radiator cooler entirely. Run the return line into the cooler inlet, keep the hose runs short, and double-clamp at each fitting. Fill and check level hot, on a level floor, with the engine running.

Heat is the single thing that kills an automatic fastest. Fluid that lives above roughly 250 F oxidizes, loses film strength, and takes the friction material and the clutch apply seals with it — which is why a truck that tows without an auxiliary cooler usually shows up with burnt fluid and a slipping direct clutch long before a truck that has one. If you tow, haul, run an RV, or live where summer stays over 90 F, this is the cheapest insurance on the unit.