Yeah, stall speed is an iffy prop. And with gear changes and tires, stall of the same converter will change. My Shelby Dakota has a factory high stall. At 3600 lbs and with 3.90 gears it should've at least been able to lay a patch, but it could barely chirp 'em. Granted, the 5.2LA was pale, but still, 270 lbs torque in a light rear? Under brake, it'd stall at 2000. Without brake, it'd flash to about 1850. Keep in mind factory transmissions are built to the last penny and clutch material in them tend to be little better than paper unless there's some sort of HD option. A low stall speed keeps the engine from ever really getting up and going, thus making life easier on the transmission. My Dak had peak torque around 2000 and it still could've used more stall. You want the engine to be able to get into the meaty torque curve. Stall too low and it's struggling until it finally overcomes the inertia enough to really pull.
As for too efficient radiators, I cannot speak to that. I'm on the MS Gulf Coast andhave never had the pleasure of that particular problem. No doubt aluminum
transfers heat much more readily than brass, but the thermostat controls the bulk of the coolant flow. Hard to imagine have an overcooled truck down south. Maybe a 3 row has too much capacity, hard to say from where I am, unable to actually see it in person. Thermostat still could be an issue. Before you go pulling the radiator out just slide a piece of sheet metal or plastic in and block off some airflow. If it's the radiator you'll see an improvement and still have max towing cooling in summer.