Stout oil for towing?

[tig1]

Use M1 in tour engine, but as others have said your transmission is the weak link. Put Mobil 1 ATF or Ams in it. Will take the heat better.

 

[3putter]

Either the PP or the Shell will do just fine, no need to change.

 

[friendly_jacek]

I used 5W40 rotella when towing with subaru during summer. Great oil. The only draw back was lower MPG in short trip city driving.

What ATF do you have? T-IV or WS? They are not that great for high temp service. I would change ATF before the trip to Redline's D4 or D6 (whichever is closed in viscosity to OEM).

The diff and transfer case need probably service too, but I would do straight SAE90 or SAE110 due to shearing of 75W90 gear oils (I had diff whine with 75W90 gear oil in subaru).