I'm moving to Mountain Green, UT in three weeks. The elevation is 5000 feet and the average high for December and January is in the upper 20's to mid 30's.

I'm getting the ball joints replaced on my 1997 4WD tomorrow, and for the sake of saving time, I'm going to have him drain and replace the the rear diff fluid. Is there any reason why I couldn't go with the 80W-140 GL-6 as he recommended, or should I stick to 75W-90?

 

I have always run 80w90 in my stuff. It's like $40 for a 5 gallon pail.

 

Unless you are towing real heavy, 75W-90 is probably the best thing to run. It is worth paying for the synthetic even though you aren't going to be in a really cold climate.

 

I have never even heard of 75w90 . I run 80w90 since I use the same gear oil in all my vehicles and it's pretty much an "all purpose" viscosity.

Synthetic is great if you can afford it. At $6-7 a quart, I can't.

 

I put synthetic in, it helps when then temps are ... minus a billion.