The coolant in the radiator flows through the engine block to keep the engine and the motor oil at the proper temperature. In some cases the manufactures have put a single thin radiator core in vehicles and there was space for adding a standard thickness core if the vehicle had the "tow package". The manufacturers charged extra for something they used to include in their trucks. This same tow package will include a transmission cooler.
Synthetics can be worse for engines operating under high temperatures. almost all of them are 5W40 formulations and the engine manufacturers specify this weight for sub zero driving conditions and air temperatures under 90F degrees. In hotter weather they specify a 15W40 motor oil regardless of whether it is a mineral/dino or synthetic motor oil. You do not want to be starting the engine with a 5W oil on a 100 degree day and waiting for it reach 15W to be properly lubricating the engine bearings.
I view towing as a severe duty use of the engine and transmission and adjust the oil and ATF service intervals accordingly. I change the oil every 7500 miles and at that interval there is absolutely nothing to gain with a synthetic even if it was the proper 15W40 oil.
25% of what goes into motor oil consists of additives and it is this mix that has the greatest impact on engine wear and longevity. The benefit of these additives decreases with engine use and so measuring only lubricity ignores this completely. Fresh oil means a fresh batch of additives as well. This is even more important with diesel engines as the changing of the motor oil takes out the soot and sludge that accumulate in the oil in the crankcase.
With transmission fluid there is a recommended replacement interval based on months as well as miles. Allison recommends replacing the ATF every 24 months or 50k miles whichever comes first if a TES 389 ATF is used, and every 48 months or 150k miles if TES 295 ATF is used. I use a ATF 295 to double the change interval for the transmission in my truck.
