Optimum transmission cooler size?

Looking to install a cooler on V6 2023 SR5. I pull a 5000 lb (loaded) RV trailer and plan to do some trips out west in the mountains. No off road rock crawling or anything super low speed anticipated. Wondering if a larger cooler might block enough airflow to cause any engine coolant temp issues. My current thinking is a bigger cooler is nearly the same work and cost as a smaller one so might as well go big like a Hayden 698. But maybe a 697 would be better to not block as much main radiator airflow? Planning to keep the flow through the in radiator transmission cooler with additional cooler in series. Is the main radiator cooling good enough it's not really a concern, at least for my conditions?

 

I think the 3rd Gens come with an adequate cooler from the factory. But I'm not positive.

5000 lbs is more than I'd want to pull with a Tacoma in the Rockies. That's close to the practical limit at lower elevation. Your engine will lose about 3% of its power for every 1000' you go above sea level. Some of those mountain passes are 10,000-12,000'. That means your engine will only be putting out 65-70% of the power it has at sea level. A lot of the level roads are at 7000'.

One tip. When you get at higher elevations, they sell 85 Octane gas as regular, 87 is mid-grade and 91 Octane is premium. DO NOT buy the 85 Octane if you are pulling a trailer. Stay with 87 Octane and 91 wouldn't hurt.

 

2023 won’t come with any air cooled transmission cooler, just the fluid to fluid one in the bottom of the main radiator. It’s a good thing to add.

 

Some time in the 2020 production year the external air to fluid cooler was no longer included by Toyota. The idea was something like that it was not needed by most and the trans temps stayed good in their tests. My 2020 SR5 does not have one. Since I only have a popup camper that is not that very heavy and has little wind drag I'm leaving it that way. If I get a bigger camper like over 3,000 pounds and plan longer trips with it I will get a fluid drain and fill done and have an Auxiliary cooler added then. It can't hurt to ensure the transmission stays at with in operating temps for longevity.