Question about Trans and Diff Fluid

[GHARP57]

So I am posing this to you guys for preferences. I am going to be changing the fluids in my trans and diffs soon.

I have a 99 Limited 4Runner

Keep in mind I may do off roading once a month or every couple of months since my truck is stock right now. Since I work at a dealership I was going to use orignially T4 since that is the factory fluid. I can get it cheaper than retail with my discounts. I was also thinking about going to WS transmission from the newer model 4runners. I got to talking to some of the technicians here and they said I can move forward just not backwards. WS is good for about 90k miles where as the T4 is less. Other thing about the WS is, it costs about 30 more dollars for a case than 24. Which do y'all recommend?

On my diffs and t-case. I was going to put pennzoil 75-90 in it since that is what we have in bulk here. any recommendations on that? I can get 6 quarts fairly cheap since it is bulk

 

[wanderMT]

Use full syn and probably never have to change again. Recently changed in different 4x4 I have and used Valvoline full syn everywhere.

 

[toyo]

I would not use the WS fluid. The WS fluid is much thinner for one reason. The discs, clutches etc were not engineered for WS fluid. I'm not saying the trans will fail if you do, but I would just stick with Type T IV.

I have been using M1 in my differentials for many years with no adverse problems.