2019 RAM 1500 Tradesman 4X2 EcoDiesel
Your post above made a great case for the difference based on low gear launch capabilities. I just can't see why the 3.21s would have more trouble cooling or pulling at the same RPMs and overall gear ratio. I think in the 40-50 MPH range, you'd be in 3rd or 4th gear with 3.21s, where they have a noticeably lower overall ratio, therefore higher RPMs (3 and 6% respectively) and "pull". I don't know if 6% higher RPMs would cause cooling problems, but the engine would pull better.Actually, real-world testing (and personal experience) shows the opposite. There's very little difference between 3.21 and 3.92 when doing the 0 - 60 test or 1/4 mile testing. The real difference is when you take a trailer (at max load) over a mountain pass. The 3.21 can't maintain speed, not even in a lower gear. I've literally had my 2015 (with 3.55 gears) slow down to 28 mph on a long steep grade. Why? Because the truck can't maintain speed, so I end up in a non-towing gear and the truck feels gutless. This is why the 3.92 EcoDiesel is rated to tow more than the 3.21 EcoDiesel.
SlowRoller, it doesn't sound like you're towing near maximum capacity and/or towing on long steep grades, so you might not have major cooling issues. If you run into cooling issues, there are three things that you can do to help.
1. Change to the honeycomb style grille if you have one of the restrictive grilles.
2. GDE offers a lower temperature thermostat that reduces coolant and oil temps about 18*F.
The 2020+ 3rd gen EcoDiesel DOES NOT have a cooling issue, which is why it's towing capacity is more closely rated to the Hemi etorque.
I haven't had major cooling issues. My oil hit 253 F once. I have the Tradesman grill and only pull around 5,000#. I have driven long, steep grades in CO and CA, but CO was in April, so not terribly hot, especially at 10,000'. Like you, I have 3.55s, so some (dis)advantages compared to the other two ratios.
On Memorial Day, we went over Donner Summit instead of our planned route to Lassen through Red Bluff and Anderson, where 109F was predicted (maybe only 104 when we would have gone through).