So, you just got a level kit and 35" tires and you tow regularly. What does this do to your transmission?
With EVERY change in final ratio of 1.0:1 your transmission temperature will increase or decrease by about 25 percent at given load, and remember, tire diameter has a direct effect on final ratio. Final or EFFECTIVE ratio is determined by the following formula: Old Tire Diameter / New Tire Diameter x Gear Ratio = Effective Ratio.
So, assuming you have 3.92 gears and go from stock size tires of say 245/70r17 to 35x12.5x17s. Your EFFECTIVE RATIO would change from 3.92 to 3.47, so if your transmission was running at about 190* with no load, it would now be running at about 212*, not a big deal. But if your transmission was running at about 220* while towing a decent load (about average) then with the 35" tires your transmission would be running at about 250* WHICH IS HOT! You don't even want to see these numbers if your truck has the stock 3.55 gears!!!
A tranny cooler will help some, but the bottom line is your transmission is still generating that much heat.

To tow well, even with 33" tires it would be very advisable to make a change to at least 4.10 gears and much taller then 4.56s would almost be a necessity. According to data provided by the American Camper Association, a stock Ram 1500 has a 1000# higher towing capacity with 4.56 gears as opposed to 3.92s given equal tire size and almost a 2000# higher capacity than 3.55 gears.

If you are towing regularly, a larger pan capable of holding more fluid would also be a good mod, as would a transmission temperature gauge...